Whilst all authority in [the federal republic of the United States] will be derived from and dependent on the society, the society itself will be broken into so many parts, interests and classes of citizens, that the rights of individuals or of the minority, will be in little danger from interested combinations of the majority. In a free government, the security for civil rights must be the same as for religious rights. It consists in the one case in the multiplicity of interests, and in the other, in the multiplicity of sects. — James Madison (The Federalist, No. 51)

The relevance of social groups and identities to American political behavior has long been noted. From the founding, the concept of pluralism, or as Madison stated, “the multiplicity of sects” in American society has been noted as a source of stability for American peace and democracy (Dahl, 1972). Recently, however, many of the social divides in American politics have moved into alignment with political parties, concentrating the “multiplicity” of social divisions along a single partisan line (Mason, 2018). One corollary of this, we demonstrate here, is an increase in the strength of citizens' affiliations with their parties. Furthermore, this effect is asymmetric across the two parties. The “correct” alignment of social identities—including White and Christian identities that are not typically mentioned in “identity politics” punditry—is more strongly related to Republican partisanship than to Democratic partisanship. In essence, we find that all politics is identity politics, including the partisan preferences of Whites and Christians.

Campbell, Converse, Miller, and Stokes (1960) characterized extrapartisan social groups as standing “at one remove from the political order. Their reason for existence is not expressly political…But members of these groups appear to think and behave politically in distinctive ways” (p. 295). The authors of The American Voter were groundbreaking in their focus on group identification as a central motivation in modern political behavior. This “Michigan School” of political behavior not only defined partisan identity as fundamental to vote choice, but they also understood party loyalty as drawn from other central social identities.

1979 1960 he will respond to new stimuli as a party member and code them properly. As time passes, his identification with the party will increase of its own accord, because the individual will find that event after event demonstrates—in non‐group matters as well as group matters now—the rectitude of his own party and the obnoxiousness of its opponent. … Individuals strongly identified with a secondary group that maintains clear political standards would show a distinctive tendency not only to identify with the prescribed party, but also to identify strongly. (p. 328, italics in original) The Michigan School was also forward‐thinking in its assessment of how social identities function in mass politics. Even before the social identity theory experiments of Henri Tajfel and John Turner (), 1 Campbell et al. () explained group identification as a concept that should be thought of as a “psychological reality” in which “there is room for a great deal of variation in the degree of psychological membership that characterizes the relationship” (p. 306). The scholars of the Michigan School also expected that social groups “formed along occupational, ethnic, or religious lines” were likely to determine a person's political attitudes, rather than their attitudes determining their group identities (p. 323). Finally, they found that if a social group membership was the reason for a person's identification with a party, that individual's identification with the party was likely to grow stronger. They explained the process by stating that once a group influence leads a person to identify with a party,

This idea that the degree of party identification can be affected by the degree of other, party‐aligned social group identifications is a key concept for understanding modern political behavior.

In the decades after the publication of The American Voter, the central relevance of social group identification in American political behavior receded. In the 1960s, cross‐cutting identities arose after the exodus of conservative Southern Democrats from the Democratic Party. Partisanship grew weaker as a political cue and other, more issue‐based cues, were identified to explain political behavior (i.e., Fiorina, 1981). The concept of “identity” in politics was either understood as a source of democratic stability, as in the pluralism literature (Miller, 1983), or as an issue‐based source of particular grievance, in which marginalized group members mobilized on behalf of particular and singular group‐preferential causes (Grossman & Hopkins, 2016).

Here, we bring the focus back to the way that voters construct their partisan identities using the aggregate alliances between party and other social identities such as religion, race, and ideology. These alliances have been growing increasingly powerful in recent decades, as we demonstrate below, in a process that Mason (2016) has called “social sorting.” This identity‐based sorting has motivated partisans to cling more strongly to their partisan groups, exacerbating the partisan social and affective polarization that has often been observed in recent years (Iyengar, Sood, & Lelkes, 2012; Iyengar & Westwood, 2015; Mason, 2015).

Traditional Identity Politics A social identity is characterized as a sense of shared identity with a particular group. According to Klandermans (2014), this sense of group identification is “an awareness of similarity, ingroup identity, and shared fate with others who belong to the same category…It has pervasive effects on what people feel, think, and do” (p. 5). This concept of social identity was originally elaborated via social identity theory, developed by Tajfel and Turner (1979). Because group identification is driven by an innate desire to positively distinguish one's ingroup, the most prominent effect generated by this process is ingroup bias, in which strongly identified group members reliably privilege and judge the members of their own group as superior to members of the outgroup, without regard to the constraints of reality. 1984 relatively few Americans think “ideologically” in the sense that they order their political beliefs according to certain basic ideological principles. Thus, as Kinder (1982) has pointed out, the key question is no longer “do people think ideologically?” but rather simply, “how do people think about politics?” In addressing this question one approach is to return to “basics,” to go back to those ideas that originally fueled research on political behavior. And, one of the more appealing of those is the notion that people's ties to various groups help to structure their political thinking. (p. 761, emphasis added) A traditional view of identity politics takes individual social identities, such as race or religion, and examines how each identity is capable of driving political behavior in relation to that specific group. As Conover () explains, Thinking about individuals' ties to their distinct social groups has been a useful way to help political scientists understand how Americans organize their political beliefs and behaviors. Klandermans (2014), for example, explains that “collective identity becomes politically relevant when people who share a specific identity take part in political action on behalf of that collective” (p. 2). In other words, social identities translate into political ones when group identities are associated with explicit, political demands (Huddy, 2015). At times, often as a replacement for ideological sophistication, a salient racial or religious identity can motivate individuals to grow awareness around and take political action on behalf of racial or religious issues, respectively (e.g., Carmines & Stimson, 1982). Yet these are inherently limited approaches to politics because the effect of an individual's particular identity on political behavior is essentially viewed in isolation from the other identities that comprise their world view. Recent work by Huddy, Mason, and Aaroe (2015) provides evidence that an individual's partisan identity can also be treated as a social one, which is to say that this identity is not entirely dependent upon logical policy‐based decisions. Bolstering this claim, Theodoridis (2013, 2017) finds evidence that partisan identity exists at an implicit level, while Iyengar and Westwood (2015) demonstrate that partisan affect is so deeply ingrained in individuals' minds that partisan identities exert powerful influence on a variety of nonpolitical judgments and behaviors. Achen and Bartels (2016) link political behavior mainly to social identities and partisan loyalties. In other words, partisan identities, like their racial and religious counterparts, are social and visceral, and they work together with other social identities to drive political judgment (see also, Green, Palmquist, & Schickler, 2002; Greene, 1999, 2002, 2004; Mason, 2013). The traditional view of these partisan, religious, racial, and even “liberal” or “conservative” identities, however, is limited by its singular focus on each social group individually. Instead of a view of identity‐related politics in which social identities are essentially compartmentalized, we suggest that the cumulative relationship between social identities and partisan identities creates a generalized politicization of Americans' otherwise nonpolitical identities. Rather than motivating increased interest in and knowledge about a small collection of issues, party‐group alliances drive people toward a broader sense of political identity that isn't limited to any one issue or group, but inspires greater partisan loyalty among the most socially sorted partisans.

History of Party‐Group Alliances In order to understand how party‐group alliances cumulatively shape partisan identity in the current political atmosphere, we first historically situate the two parties' particular racial, religious, and ideological affiliations. For decades, the “White establishment” (i.e., White, Protestant Christians) was the conventional norm among political leaders, and the “default” social identity for Americans (Theiss‐Morse, 2009). When both parties' elites predominantly reflected this “White establishment,” their members were generally (though not equally) distributed across race and religion (Abramowitz, 2013; Lewis‐Beck, Jacoby, Norpoth, & Weisberg, 2008; Zingher, 2014). This broader racial distribution ended when enfranchised African Americans (Black & Black, 1987; Tesler & Sears, 2010) and Latino immigrants (Huddy, Mason, & Horowitz, 2016) largely joined the Democratic Party. Figure 1 presents the partisan divide between Whites, Blacks, and Hispanics over time, using the American National Election Studies (ANES) cumulative file through 2012 and the 2016 ANES, constrained to face‐to‐face interviews to maintain comparability. Figures 1 through 3 are constructed by first identifying the percentage of each group in each party (i.e., Whites made up 82% of the Democratic Party in 1972, compared to 95% of the Republican Party). Each point represents the difference between the two parties on this measure (in the White race example, we subtract 0.82 from 0.95 and end up with 0.13). Above the zero line, the Republican Party has a higher percentage of group members than the Democratic Party, and the degree of the difference is represented by the magnitude of the score. Under the zero line, the Democratic Party has a higher percentage of group members than the Republican Party. As depicted in Figure 1, Democrats transformed into a more diverse combination of ethnicities and races, while Southern Whites left the party that once represented their racial “coalition of the whole” (Green et al., 2002) to join the Republican ranks. Figure 1 Open in figure viewer PowerPoint Party‐race alignments in the American electorate. Lines represent the percentage of Republicans that are members of the racial group minus the percent of Democrats who are members of the racial group. Sample weights applied; only face‐to‐face surveys used in 2016. Religious identity further reshaped partisanship (Abramowitz, 2013; Ellis & Stimson, 2012; Layman, 2001), as Republicans became the predominant party of Christians. As the Evangelical Right mobilized their constituents (Conger, 2009; Williams, 2012), individuals' level of religiosity, rather than their religious denomination, predicted their partisanship (Abramowitz & Saunders, 2006; Mohseni & Wilcox, 2009). In turn, Republican elites appealed to religious Protestants using words (e.g., “faith,” “pray,” “sacred,” “church,” and “worship “) that differentiated them from Atheists, nonpracticing Christians, and other secular Americans (Campbell, Green, & Layman, 2011; Domke & Coe, 2008; McDermott, 2009; McLaughlin & Wise, 2014). This “religious code” allowed citizens, regardless of their political awareness, to recognize which party shared their religious identity (Campbell et al., 2011). Figure 2 presents the partisan divisions between Christians and nonreligious Americans over time, with seculars increasingly growing closer to the Democrats, particularly over the past decade, and Protestants growing closer to Republicans. Figure 2 Open in figure viewer PowerPoint Party‐religion alignments in the American electorate. Lines represent the percentage of Republicans who are members of the religious group minus the percent of Democrats who are members of the religious group. ANES sample weights applied; only face‐to‐face surveys used in 2016. Finally, and perhaps most widely reported, Democrats and Republicans have grown increasingly aligned with the ideological groups “liberals” and “conservatives.” A great deal of recent research has established that ideological identities are, in fact, separate from a constrained and extreme set of policy attitudes (Ellis & Stimson, 2012; Kinder & Kalmoe, 2017; Malka & Lelkes, 2010; Mason, 2015). The identity behind these ideological labels can function as a social identity much like a racial or religious identity does. As partisan and ideological identities move into alignment (Levendusky, 2009), the same increase in partisan identity should be visible. Figure 3 presents these trends of alignment between partisan and ideological self‐identification. Figure 3 Open in figure viewer PowerPoint Party‐ideological identity alignments in the American electorate. Lines represent the percentage of Republicans who are members of the ideological group minus the percent of Democrats who are members of the ideological group. Sample weights applied; only face‐to‐face surveys used in 2016. Taken together, Figures 1 through 3 empirically demonstrate the sorting of Blacks, Hispanics, Seculars, and Liberals into the Democratic Party, and Whites, Christians, and Conservatives into the Republican Party, across the electorate. Democrats moved from a coalition empowering Whites to one of diversity and nontraditional groups, while Republicans reinforced their homogeneous White Christian conservative profile, creating easily accessible cues about who each party represents. This led to a generally accepted understanding of the Democratic Party as one of racial diversity, religious secularism, and liberalism, while Republicans were typically seen as White, Christian conservatives. Citizens could use these cues to perceive their party identity as a singular social identity (Huddy et al., 2015; Iyengar et al., 2012; Mason, 2016; Nicholson, 2012) that encompasses their ideological, ethnic, and religious affiliations. These party‐group alliance cues could alert individuals to social diversity within their party and allow them to perceive their own social ingroups as allied or unallied with the parties. Furthermore, the more diverse Democratic alliance would lead to a general tendency among Democrats to be open to religious or racial outgroup members, as their party is allied with multiple racial and religious groups (e.g., Blacks, Hispanics, Atheists) that each comprise only a fraction of all Democratic identifiers.2 For Republicans, on the other hand, the general White, Christian conservative alliance with the party led to a far simpler categorization of who is in the group and who is outside of it. This is consistent with the findings of Grossman and Hopkins (2016), who argue that Democrats are generally driven by policy‐based achievements for their varied social groups, while Republicans are more focused upon a type of “purity” where the party is represented by the “correct” groups. The asymmetry between the parties in their social diversity would predict an asymmetry in partisans' sensitivity to the social makeup of the parties. Despite the widespread knowledge of the particular social group affiliations now associated with each party (i.e., Black, Hispanic, nonreligious, liberal Democrats, and White Christian conservative Republicans), little work to date has assessed the importance of the cumulative alliance between racial, religious, and ideological groups and the parties. Brader, Tucker, and Therriault (2014) have used these “social group intersections” in their measure of political cross‐pressures, but this was tabulated by counting two‐party presidential vote shares, and their measure was not examined in relation to party identification. Additionally, Stubager and Slothuus (2013) specified that the power of partisan “issue ownership” depends on the specific groups that make up each party, where the groups themselves have power to affect parties' perceived alliances, via voters' memories. Other than these two examples, the connection between party and groups has generally been described or assumed, not empirically tested.

Objective and Subjective Social Sorting Building upon the party‐group alliances discussed above, we examine what occurs when an individual's partisan social identity becomes allied with her racial, religious, and ideological identities. There are good reasons to expect that a conglomeration of social identities that are aligned with partisan identities should have particularly profound effects on the American electorate. Klandermans (2014) notes, for example, that individuals possess multiple identities, and that “these many identities do not necessarily work in the same direction” (p. 2). What happens when these identities are discordant? 1944 1960 1960 1976 1960 1972 2012 2009 1983 All societies are divided to some degree. But some societies, especially larger and more complex ones, are divided by a pluralism of cleavages that are often related to one another in a cross‐cutting rather than reinforcing pattern. The superposition of this multiplicity of crosscutting partitions is a fine partition of society into a large number of relatively small preference clusters. Two random individuals, therefore, most likely belong to different preferences clusters and, if so, have conflicting preferences with respect to one or more issues but almost certainly agree on many issues as well. (p 735) Some early work in political science has explored the possibility that multiple identities may weaken partisanship if they are not all well‐aligned with the same party. Dubbed “cross‐pressures,” Lazarsfeld, Berelson, and Gaudet () and Campbell et al. () argued that at any given moment, voters are subject to the countervailing pressures of a number of salient social identities. For example, partisans who identify with groups associated with the opposing party are less likely to vote (Campbell et al.,), while other research suggests that these individuals are less strongly partisan (Powell,) and that these “cross‐cutting cleavages” mitigate social conflict (Lipset,; Nordlinger,), destabilize judgments and decision‐making (Lavine, Johnston, & Steenbergen,), and can lead to partisan defection (Hillygus & Shields,). This is because, as Miller () explains, This pluralist interpretation implies that as long as the social divisions in society are cross‐cutting, partisans of opposing parties should still be able to coexist in relative peace. However, once these cleavages begin to align along a single dimension, partisan conflict is expected to increase substantially. In fact, research by Mason (2016) has found that cross‐cutting social and partisan identities can significantly diminish angry responses to political messages. Related research in social psychology further supports these findings; the effect of overlapping social identities on judgment and behavior goes beyond the effect of a single social identity alone.3 When a large portion of the members of one group are (or are believed to be) also members of another group, individual members are more likely to be intolerant, biased, and feel negatively toward outgroups (i.e., those who are not in your group) (Brewer, 1999; Roccas & Brewer, 2002). Conversely, when group identities are cross‐cutting, or “complex,” individuals are generally found to be more tolerant, less biased, and feel more positive emotions toward outgroups. This is because cross‐cutting identities reduce the perceived differences between the groups and allow an individual to feel like she belongs to and is defined by a broader range of groups (Roccas & Brewer, 2002). These are psychological effects of party‐group alliances that deal with the perception of innate differences, rather than the thoughtful considerations of issues. Once we conceptualize partisan identities as social identities that have the capacity to align with or diverge from other identities, it is possible to predict that a member of a party that is unaligned with their religion, race, or ideology (e.g., a White, conservative Democrat) would feel less affective attachment to their own party than a member of the same party whose religion, race, and ideology are completely aligned with their party (e.g., a Black, atheist, liberal Democrat). The alliances between groups and parties can therefore be quite psychologically powerful. We conceptually define this portfolio of social and partisan identities as objective social sorting, wherein personal attachments to each of the objectively aligned racial, religious, ideological, and partisan groups merge to create more loyal partisans. These objective connections, and an implicit understanding of their existence, underlie the measurement strategy of Mason (2015, 2016), who examines the effects of increasingly aligned partisan and social identities on emotional reactivity and social polarization. Furthermore, by this logic, the party with the most homogenous social makeup (i.e., Republicans) should be more responsive to objective social sorting—responding to party‐consistent identities with more ingroup bias, and to party‐inconsistent identities with significantly less ingroup favoritism. 2002 perceived between various pairs of groups, a subjective understanding. Back in 1954, Berelson, Lazarsfeld, and McPhee found that, actual cleavage within the community is deepened by the voter's perception of it. Differences in perception are a product of social stratification, and they reinforce it. Perceptual distortion increases the objective differences between “we” and “they.”… This makes for a unidimensional or monolithic distinction between the good people and the bad people (in religion, in status, in culture, and in politics), and it is a danger to a pluralistically organized democracy. (p. 86) While we expect belonging and feeling close to groups that are associated with the parties should increase partisan social identification, the mechanism remains unclear. Do individuals in fact realize that their ingroups and parties are aligned? The literature that first examined the effects of identity alignment on prejudicial behavior toward outgroups (Roccas & Brewer,) used a measure that explicitly gauged the respondents' own knowledge about the relationship between their multiple identities. The alignment, or social sorting of identities, was originally measured by asking respondents directly how much alignment theybetween various pairs of groups, a subjective understanding. Back in 1954, Berelson, Lazarsfeld, and McPhee found that, Further, Ahler and Sood (2017) found that this subjective understanding has the potential to increase partisanship and polarization and that correcting any inflated sense of alignment can work to reduce this partisan bias. As such, party‐group alliances should only lead to stronger partisan attachment when individuals can successfully perceive the cumulative alignment between their ingroups and in‐party—what we conceptually define as subjective social sorting. Indeed, from a social identity complexity (Roccas & Brewer, 2002) standpoint, the reason such objective group pairings work is because individuals cognitively conceptualize their ingroup members as matching with their fellow party members. As such, increases in the cognitive overlap across multiple ingroups and one's party create a strong, overarching sense of party identity. This type of superordinate party identity wherein your racial, religious, and ideological ingroups have coalesced around your party should lead to greater in‐party attachment. Further, such subjective perceptions of social sorting are necessary for demographic groups that may otherwise be split across the parties—including Whites and Christians. Members of these groups split their affiliations across the Republican and Democratic Parties. However, according to social identity complexity theory (Roccas & Brewer, 2002), the closeness that people perceive between these groups and the parties can vary significantly. This variation in subjective perceptions of how the parties align with groups, and how close people feel their ingroups are to their copartisans should create the psychological underpinnings required to motivate in‐party favoritism. 1979 2002 1) Closeness to multiple party‐aligned groups will enhance party identity strength. The more party‐aligned racial, religious, and ideological groups a person is close to, the stronger their party identity. In contrast, if one is close to unaligned groups, this creates cross‐pressure between party and group identity, weakening party identity.

Closeness to multiple party‐aligned groups will enhance party identity strength. The more party‐aligned racial, religious, and ideological groups a person is close to, the stronger their party identity. In contrast, if one is close to unaligned groups, this creates cross‐pressure between party and group identity, weakening party identity. 2) The stronger a person's identification with multiple party‐aligned groups, and the stronger their party identity (i.e., objective social sorting), the warmer they will feel towards copartisans. As all party and groups memberships come into alignment and one feels close to these groups, they will express increased affective attachment to the party.

The stronger a person's identification with multiple party‐aligned groups, and the stronger their party identity (i.e., objective social sorting), the warmer they will feel towards copartisans. As all party and groups memberships come into alignment and one feels close to these groups, they will express increased affective attachment to the party. 3) Alternatively, the more a person psychologically understands the party‐group alignment, and cognitively connects the members of their racial, religious, and ideological groups with the members of their party (i.e., subjective social sorting), they will express increased affective attachment to the party. This would occur whenever a person psychologically connects the members of their racial, religious, and ideological groups to their copartisans, even if this is objectively incorrect.

Alternatively, the more a person psychologically understands the party‐group alignment, and cognitively connects the members of their racial, religious, and ideological groups with the members of their party (i.e., subjective social sorting), they will express increased affective attachment to the party. This would occur whenever a person psychologically connects the members of their racial, religious, and ideological groups to their copartisans, even if this is objectively incorrect. 4) These sorting mechanisms should work in conjunction such that those who psychologically connect their groups to their party (i.e., subjectively sorted) and feel close to the correct party‐aligned groups (i.e., objectively sorted) should exhibit the greatest amount of in‐party affective attachment.

These sorting mechanisms should work in conjunction such that those who psychologically connect their groups to their party (i.e., subjectively sorted) feel close to the correct party‐aligned groups (i.e., objectively sorted) should exhibit the greatest amount of in‐party affective attachment. 5) Finally, we assess any possible asymmetry of these sorting mechanisms across the parties, in order to determine whether party‐group alliances have a larger effect on Democrats' or Republicans' partisanship. The ingredients of partisan identification may be a synthesis of objective social sorting that citizens need only understand at the implicit level, with subjective perceptions of party‐group attachment acting as an identity enhancer. While it has been assumed that individuals understand the parties, and form their party identities, on the basis of which social and demographic groups each party represents, this process has never been formally defined or empirically tested. The current study seeks to do so. As racial, religious, and ideological groups become more aligned with the parties, we should expect a person's membership in aligned groups to increase the strength of their party identity. Further, this effect should be cumulative—the more your religious, racial, and ideological identities concurrently align with your party identity, the stronger your party identity should become. Building upon social identity theory (Tajfel & Turner,) and social identity complexity theory (Roccas & Brewer,), we should expect the following:

Methods Data We use two datasets to assess the roles of party‐group alliances and social sorting on partisanship at two time points in recent American politics. The first dataset comprises a nonprobability Internet sample (N = 754), where respondents were recruited through the online classifieds website BackPage.com and Mechanical Turk during the summer of 2013 (hereafter referred to as the “Internet study”). This sample is representative of nonprobability Internet samples (Berinsky et al., 2012). Respondents were more likely to be male (54.64%) and White (71.88%) but also included African Americans (7.82%) and Hispanics (7.29%). This sample was younger (66.45% under 35 years old), more secular4 (48.81% atheist or no religious affiliation), and more educated (50.53% holding at least a bachelor's degree) than the general population. Politically, respondents leaned liberal (65.78%) and Democrat (65.12%). Despite its skew, this sample serves as a baseline that reflects a noncampaign year during Obama's presidency. We supplement the nonprobability Internet sample with data from the 2016 Cooperative Congressional Election Study (CCES) University of Mississippi module (Dowling, 2016), allowing us to observe the dynamics of party‐group alliances during Donald Trump's presidential campaign, and among a nationally diverse sample. The CCES, administered by YouGov/Polimetrix and fielded October 2016, is an opt‐in Internet‐based survey that uses a combination of sampling and matching techniques to account for the fact that opt‐in Internet survey respondents may differ from the general population. This sample (N = 1000) resembled the U.S. population in terms of gender (53% women, 47% men), and race (71.7% White, 12.6% Black, 6.6% Hispanic) but was slightly less Christian (36.44% Protestant) and more secular (32.1%) than the nation. Further, the sample skewed a bit Democratic (46.2% Democrats, 16.6% Independents, and 34.1% Republicans), though evenly distributed across ideology (33.4% Liberal, 28.35% Moderate, 38.25% Conservative). Importantly, given the inherent distinctions between these two samples (a nonprobability Internet sample in a nonelection year versus the 2016 CCES), any heterogeneity found across samples merely reflects these differing sampling strategies and not any substantive temporal changes in the population. Objective social sorting Our first social sorting variable, objective sorting, assesses not only the respondent's collection of racial, religious, and ideological groups and their relation to the respondent's party, but also includes the degree to which the respondent identifies with each of these groups. Our measure uses group‐identification language based on that introduced by Miller, Gurin, Gurin, and Malanchuk (1981). In the CCES we asked respondents, “Of the following groups how close do you feel towards them? By ‘close’ we mean people who are most like you in their ideas, interests, and feelings.” Groups included in the measure were Whites, Blacks, Hispanics, Atheists, and Christians. For each group, respondents chose from four options ranging from “very closely” to “not closely at all.” The Internet study used a proxy of this closeness item, first asking respondents to select their racial, religious, and other social identities,5 then rank all selected identities from most to least important. For the purposes of this measure, we include respondents' rankings of their White, Black, Hispanic, Atheist, and Christian identities.6 Since respondents were asked about seven different social groups, each group ranking could range from 1(most important) to 7 (least important). Closeness to ideological groups (i.e., Liberals or Conservatives) in the CCES was captured through self‐placement on the 7‐point ideology scale, in line with measures of symbolic ideology (Ellis & Stimson, 2012) and ideological identity (Mason, 2015). The Internet study applied a more nuanced measure of attachment to ideological groups, with a four‐item battery that assessed the strength of liberal and conservative identities, similar to measures of partisan social identity (Huddy et al., 2015, see the online supporting information). Responses to each group closeness item were recoded 0–1, where 1 represents the most attachment or highest ranking, and 0 the least amount of attachment or lowest ranking. Our objective sorting variable was then constructed by taking the mean of these social identities, with reference to their current party‐group alignment. As established in Figures 1 through 3, Democrat‐aligned groups include Black, Hispanic, Atheist/No Religion, and Liberal, while Republican‐aligned groups include White, Christian, and Conservative. Party‐congruent identities were coded positively, and cross‐cutting identities recoded negatively. For instance, an African‐American Democrat who felt very close to Blacks would be coded +1 for this racial identity, while an African‐American Republican who strongly identified with Blacks would be coded −1 for this racial identity. As such, each group rating could range from −1 to +1 depending on the amount of closeness to the group, and whether the group was aligned with the respondent's party. We also include party identity strength in this calculation, using the folded 7‐point party identity scale, 0 = pure independent and 1 = strong partisan. However, since we are only interested in how individuals use their social groups to make sense of their Democratic or Republican identity, we exclude pure independents (N = 110 in the Internet sample; N = 166 in the CCES) when constructing the full scale. Once all group ratings and party identity strength were averaged together, the objective sorting variable was recoded to range from 0 to 1. A score of 1, therefore, indicates strong identification with the political party, as well as strong identification with all party‐congruent groups, and no cross‐cutting groups. A score of −1, in contrast, indicates a weak identification with the party, strong attachment to cross‐cutting groups, and no identification with party‐congruent groups. Generally speaking, most respondents fall around the midpoint of this objective social sorting scale (Figure 4). Yet, we also observe an asymmetry across parties in how individuals objectively sort into “party‐group alliances.” Republicans are significantly more sorted than Democrats, with a difference that ranges from about 4% (p < .01) in the Internet sample to about 17% (p < .01) in the CCES, on the 0–1 scale. Further, objective sorting is skewed in both studies such that extremely few Democrats and no Republicans exhibit complete cross‐pressure across their social and partisan identities. Put plainly, there exist no Black, Atheist, Liberal Republicans, nor many White, Christian, Conservative Democrats who feel close to their groups and identify weakly with their party. Still, Democrats appear to navigate cross‐cutting identities within their party more frequently than Republicans, whose racial, religious, and ideological identities better converge with their party identity. Figure 4 Open in figure viewer PowerPoint Properties of objective social sorting by party. [Color figure can be viewed at wileyonlinelibrary.com] In order to examine the relationship between identification with social groups that are aligned with the parties and party identity strength, we also created a measure of “party‐aligned group closeness.” This measure uses the same items and coding scheme as our objective sorting scale with one exception, it excludes folded party identity from the overall calculation. Unsurprisingly, the party‐aligned group closeness scale is similarly distributed and reflects the same party asymmetry, as the objective sorting measure (see the online supporting information). While the both objective sorting and party‐aligned group closeness measures take account of the degree of identification with each objectively aligned group, they do not provide information about whether the respondent understands whether these identities are objectively aligned with their party. Subjective social sorting Subjective perceptions of sorting among one's ingroup members and their party members are measured through items that ask individuals to cognitively map overlap between multiple group identities. We assess this overlap through items derived from the social identity complexity scale (Roccas & Brewer, 2002). The Internet study asked: “Of people who are [racial, religious, or ideological group members], how many would you say are also [Republicans/Democrats]?” Respondents' perceptions of overlapping group members were then rated on a 5‐point Likert scale from “none” to “almost all.” Similarly, the CCES asked: “How closely do you associate the following groups with the [Republican/Democratic] Party? By ‘closely’ we mean people who are most similar in their ideas, interests, and feelings.” Respondents then reported their perceptions of closeness on a 4‐point Likert scale from “not closely at all” to “very closely.” In both studies, these items are asked for the following groups: Whites, Blacks, Hispanics, Atheists, Christians, Liberals, and Conservatives. However, we only use perceptions of the racial, religious, and ideological groups that individuals belong to, and only in relation to the party they identify with. This means for a White, Christian, Liberal Democrat, we only use her perceptions of alignment between Whites, Christians, and Liberals with members of the Democratic Party.7 Additionally, as we are interested in how individuals perceive alignment between their social groups and the party they belong to, we only include Democratic and Republican identifiers in this scale. These reported perceptions were averaged across all racial, religious, and ideological groups to create the subjective sorting scale, which reflects the cumulative perceptions of alignment between one's ingroups and their party. This scale ranges from 0 to 1, where 0 = no perceived overlap between any social ingroups and one's party, and 1 = perceptions of complete overlap between all social ingroups and one's party. Accordingly, the more one feels that their racial, religious, and ideological groups are closely aligned with their party, the higher their subjective sorting score will be. Further, this score is agnostic to any objective group allegiances with the parties. A person can be objectively unsorted (e.g., Black Republican or Christian Democrat) but still express closeness between her ingroup members and her copartisans. In this way, individuals in demographic groups that may be split across the parties can still sort themselves into the parties (see Table 1). For example, while numerically, more Whites identify as Democrats than Republicans in the CCES, White Republicans, on average, perceive more subjective overlap between their ingroups and party (0.705 on the 0–1 scale) than White Democrats (0.598 on the 0–1 scale). Thus, while in a particular sample there may be more Whites in the Democratic Party, they may not cognitively perceive the group to be necessary for a strong party identity. Table 1. Mean Subjective Sorting by Social Group and Party ID Whites Blacks Hispanics Atheists Christians Liberals Conservatives Republicans Internet Sample 0.67 (N = 131) 0.625 (N = 1) 0.444 (N = 9) 0.546 (N = 36) 0.698 (N = 56) 0.458 (N = 18) 0.717 (N = 113) Republicans CCES 0.705 (N = 279) 0.531 (N = 7) 0.661 (N = 20) 0.529 (N = 61) 0.716 (N = 166) 0.381 (N = 10) 0.748 (N = 250) Democrats Internet Sample 0.697 (N = 327) 0.708 (N = 51) 0.704 (N = 38) 0.72 (N = 273) 0.677 (N = 82) 0.723 (N = 438) 0.523 (N = 18) Democrats CCES 0.598 (N = 288) 0.725 (N = 100) 0.735 (N = 36) 0.611 (N = 166) 0.615 (N = 146) 0.702 (N = 279) 0.579 (N = 61) Though the objective and subjective sorting measures are conceptually related, the empirical relationship between being objectively sorted into a party‐group alliance and possessing a subjective perception of that alliance is moderate (Internet sample r = 0.365, p < .01; CCES r = 0.35, p < .01). As a result, even individuals who are not members of the party‐aligned groups can feel like their group members do, in fact, reflect the demographic fabric of their party. Further, individuals in both parties consistently report subjective sorting scores above the midpoint of the 0–1 scale (Figure 5). Unlike the objective sorting measure, party asymmetry in the subjective sorting scores is inconsistent across samples. In the Internet sample, subjective sorting is, on average, higher among Democrats than Republicans, by about 5% (p < .01) of the scale, meaning that Democrats perceive more of their ingroups as aligning with their party. Yet in the CCES, Republicans express, on average, about 4% (p < .05) more subjective sorting than Democrats. The distributions of subjective sorting also differ across samples. In the Internet sample, Republicans exhibit a wider range of party‐group alliance perceptions, compared to Democrats who mostly fall at the high end of the scale, believing that most of their ingroups are aligned with their party. Yet, in the CCES, Democrats and Republicans have similar distributions of subjective sorting. Figure 5 Open in figure viewer PowerPoint Properties of subjective social sorting by party. [Color figure can be viewed at wileyonlinelibrary.com] In‐party attachment We use in‐party feeling thermometer ratings as our main dependent variable of party attachment. Respondents were asked to rate their feelings towards the Democratic and Republican parties on 10‐point scales in the Internet study, and on 7‐point scales in the CCES, with all scales recoded 0 (cold) to 1 (warm). Feelings towards one's in‐party were calculated as an additive scale that included Democrats' ratings of the Democratic Party, and Republicans' ratings of the Republican Party, with pure independents excluded. Generally, partisans felt warm towards their own party (Internet sample M = 0.656, SD = 0.24; CCES M = 0.667, SD = 0.26). We also measure party identity strength captured via the folded 7‐point party identity scale. Since we limit all of our sorting measures and analyses to partisan identifiers only, this scale effectively ranges from .33 (leaning partisan) to 1 (strong partisan) (Internet sample M = 0.68, SD = 0.26; CCES M = 0.75, SD = 0.27). As it is a key component of our objective sorting measure, party‐identity strength is only utilized as a dependent variable when testing the effects of party‐aligned group closeness. Control variables. All models employ the standard controls used in assessing political behaviors, including gender (female = 1), age (Internet sample M = 18–34 years old; CCES M = 48.4 years old, SD = 16.75 years), education (coded 1 = obtained at least a Bachelor's degree, and 0 = otherwise in the Internet sample; and ranging from 1 = no high school, to 6 = post grad degree, M = 3.73, SD = 1.48 in the CCES), and income (Internet sample median = $40–50k; CCES median = $50–59k). We gauged political interest by asking “How interested are you in information about what's going on in government and politics?” on a 5‐point scale from 0 (not interested at all) through 1 (extremely interested) (M = 0.584, SD = 0.265) in the Internet study; and in the CCES through the frequency of reading about political news on a 4‐point scale from 1 (Hardly at all) to 4 (Most of the time) (M = 3.185, SD = 0.97). Finally, in the CCES only, we gauged political knowledge using two questions that asked respondents to identify the majority party in the House and Senate, respectively, and scaled together such that 0 (no questions correct) and 1 (both questions correct) (M = 0.607, SD = 0.442).

Results Aligned Group Membership and Party Identity Strength We begin by assessing the relationship between individuals' racial, religious, and ideological identities and the strength of their party identity. If a person is technically a member of a group that they don't feel particularly close to, that identity has little power to affect their beliefs and behavior. In contrast, strong attachment to a social group increases the salience of that identity. Thus, those who belong and feel closer to party‐aligned groups (e.g., Whites, Christians, and Conservatives for Republicans, and Blacks, Hispanics, Atheists, and Liberals for Democrats), should also hold a stronger party identity, and vice versa.8 In contrast, those who are closely attached to groups that are not aligned with the parties (e.g., Black, Hispanic, Atheist, Liberal Republicans, or White, Christian, Conservative Democrats) experience cross‐cutting pressures which should weaken party identity strength. Figure 6 depicts this expected pattern.9, 10 In the CCES, attachment to party‐aligned groups is significantly related to party identity strength, albeit asymmetrically across parties. Among Democrats, as attachment to aligned racial, religious, and ideological groups increases, party identity strengthens, on average, by .24 (p < .05) on the 0–1 scale. This relationship among Republicans, however, is much more powerful, with increases in group attachments relating to an increase in party identity strength by nearly two‐thirds of the 0–1 scale (β = 0.659, p < .01). This heterogeneity makes intuitive sense. The Democratic Party encompasses a greater variety of groups, making cross‐cutting identities less detrimental to Democrats' party identity, relative to Republicans who have fewer associated groups and more identity‐based “deal‐breakers.” Interestingly, such asymmetry is absent in the Internet sample, where closeness to party‐aligned groups relates to an increase in party identity by only about 20% of the scale for both Democrats and Republicans.11 Nonetheless, Figure 6 highlights how racial, religious, and ideological group attachments serve as an ingredient of partisan strength, particularly among Republicans, whose strong partisans are those closest to the “correct” groups. Figure 6 Open in figure viewer PowerPoint Effects of party‐aligned group closeness on party identity strength. [Color figure can be viewed at wileyonlinelibrary.com] Social Sorting and In‐Party Attachment Having established that attachment to party‐aligned groups is associated with partisan strength, we next examine the role of objective sorting, the process by which individuals feel more closely attached to the specific groups aligned with the party and with the party itself. When individuals exhibit greater objective sorting, we should also observe increased attachment to their party. In the Internet sample (Figure 7, left panel), objective sorting significantly relates to warmer in‐party feeling thermometer ratings for Democrats by about 30% of the scale (β = 0.31, p < .01), and Republicans by about 45% of the scale (β = 0.46, p < .01). Similarly, in the CCES (Figure 7, right panel), objective sorting is related to Democrats' increased feelings of in‐party warmth, on average, by about 20% of the scale (β = 0.22, p < .01). This relationship between objective sorting and in‐party feelings is even stronger among Republicans,12 related to a 40‐percentage‐point increase in the feeling thermometer (β = 0.39, p < .01). Figure 7 Open in figure viewer PowerPoint Effects of objective sorting on in‐party closeness. [Color figure can be viewed at wileyonlinelibrary.com] Despite similar associations between objective sorting and in‐party ratings across the two parties, Democrats, on average, feel warmer toward their party regardless of their level of objective sorting. This difference across partisan groups is most predominant amongst the least objectively sorted, where Democrats holding the most cross‐cutting identities in both samples remain relatively affectionate toward their copartisans (around 0.5 and 0.7 on the 0–1 scale, respectively). In contrast, Republicans who feel close to the racial, religious, and ideological groups who are not aligned with the party, typically express cooler reactions towards the Republican Party in both samples (approximately 0.2 and 0.4 on the 0–1 scale, respectively).13 Yet, Republicans who feel close to the “correct” party‐aligned groups are just as warm towards their copartisans as Democrats. This supports our theory that Republicans are generally more sensitive to who does and does not “belong” in the party. Republicans who are ideological, racial, or religious “outsiders” feel less connected to the party than do Democrats who don't fit in. Our objective sorting measure, however, cannot assess whether individuals psychologically understand the connections between their social groups and their party. We know that social identities become more psychologically durable as multiple ingroups converge on a singular identity that subsumes all others (Roccas & Brewer, 2002). Thus, when individuals cognitively map their racial, religious, and ideological identities onto their party identity, a process we define as subjective social sorting, we would also expect them to express warmer feelings toward their copartisans. Subjective sorting is positively related to in‐party feeling thermometer ratings equally across parties in both samples (Figure 8). When moving from the least to most amount of perceived party‐group overlap in the CCES sample, in‐party feeling thermometer ratings increase, on average, by about 18% of the scale (β = 0.177, p < .01 for Democrats and β = 0.176, p < .01 for Republicans). A similar, yet stronger, pattern emerges in the Internet sample, where subjective sorting perceptions are related to larger increases in in‐party feeling thermometer ratings among Republicans (β = 0.315, p < .01) than among Democrats (β = 0.212, p < .01), though the difference between slopes is nonsignificant. As with the objective sorting models, we again discover a significant party effect, such that Democrats, regardless of their level of subjective sorting, feel warmer towards their copartisans than Republicans.14 Figure 8 Open in figure viewer PowerPoint Effects of subjective sorting on in‐party closeness. [Color figure can be viewed at wileyonlinelibrary.com] Our results indicate that objective and subjective sorting, in isolation, are associated with more intensely positive feelings towards one's in‐party. But it is possible that these two sorting mechanisms work in tandem with one another, and as such, we examine the interactive effects of these sorting measures on in‐party feeling thermometer ratings. Since we did not observe any significant differences in slopes in the relationship between either sorting measure and party closeness, we examine the conditional relationship between objective and subjective sorting for Republicans and Democrats combined. We find a significant conditional relationship between objective and subjective sorting, at least in Internet sample (Figure 9, left panel). The partisans who exhibit the most warmth towards their party are the ones who are the most objectively and subjectively sorted. Subjective sorting has no relationship with in‐party ratings among individuals who do not feel strongly associated with the party‐aligned groups, while objective sorting has no bearing on those who do not perceive overlap in members of their groups and their party. Yet, when individuals feel closer to party‐allegiant groups, perceptions of group‐party alignment are related to an increase in in‐party feelings by about 20% at the objective sorting median (p < .01) and nearly 40% at the 95th percentile of objective sorting (p < .01). Among those who perceive overlap between their racial, religious, and ideological groups and their party, those close to the correctly aligned groups exhibit stronger in‐party feelings than those with cross‐cutting identities by almost half of the scale (β = 0.481, p < .01). Put simply, the strongest, most attached partisans are the ones who identify with the correctly aligned groups and consciously understand that correct alignment. Figure 9 Open in figure viewer PowerPoint Effects of objective and subjective sorting on in‐party closeness. [Color figure can be viewed in the online issue, which is available at www.laryngoscope.com.] The CCES sample, in contrast, presents an alternate story (Figure 9, right panel). Subjective sorting is, on average, associated with more in‐party support, but only among those who are not objectively sorted (β = .19, p < .05 and β = .14, p < .01 for those at the 5th and 50th percentiles of the objective sorting measure, respectively). Among the objectively sorted—those strong partisans who feel closely attached to their party's allegiant groups—cognitively acknowledging these party‐group connections contributes nothing to their feelings of party closeness. In further divergence from the Internet sample, there is no significant relationship between level of objective sorting and in‐party feelings, nor is the interaction between the sorting measures significant. In short, those who feel close to their copartisans are either attached to the correctly aligned racial, religious, and ideological groups or cognitively understand the alignment between their groups and their party. Given these inconsistent findings across samples, though objective and subjective social sorting processes are clearly linked to in‐party affective attachment, their operation in combination remains ambiguous.