“Every difference of opinion,” Thomas Jefferson warned in his first inaugural address, “is not a difference of principle.” Speaking to his countrymen after an election every bit as bitter as the one that put Donald J. Trump in the White House, Jefferson was trying to soothe the reigning animosity between the nation’s two dominant political parties. “We are all Republicans,” he added. “We are all Federalists.”

Not anymore. In 21st century America, any notion that election results end the argument, however temporarily, is an anachronism. So, too, is the conceit that a nation this large and diverse is divided neatly along “50-50” lines, with half of America’s 253 million adults supporting Democrats, and the other half backing Republicans.

Today, slightly more than one-fourth of registered voters in the United States have political views and social attitudes placing them in the camp of the “Resistance” -- to President Trump and the Trump-era Republican Party.

This is one of the five American “tribes” identified in a sweeping new public opinion survey conducted by RealClear Opinion Research, a new service offered by RealClearPolitics. The survey of 2,463 registered voters, conducted Sept. 18-28, was overseen by John Della Volpe, co-founder of SocialSphere Inc., a public opinion and analytics firm based in Cambridge, Mass.

On the other side of the spectrum are two “tribes” of Trump voters, roughly evenly divided, which together make up another quarter of the electorate. One of these groups (12 percent) is the Trump base -- the “Make America Great Again” crowd that attends his rallies and idolizes his brand of conservative populism. The other (14 percent) consists of traditional Republicans with less edgy views on issues ranging from trade to immigration to race relations.

A fourth group, which Della Volpe has dubbed “The Detached,” is even harder to peg. This segment is the youngest of the five, and the most male. They tend to be disillusioned, even disgusted, by party politics, and represent 24 percent of registered voters in the United States.

A fifth cohort, the “Independent Blues,” is the most pivotal group. In 2016 they cast their ballots for Hillary Clinton by a 12-percentage-point margin, and their skepticism toward Republicans has only grown in the ensuing two years. Just 16 percent of them say there is a strong likelihood they’ll vote for Donald Trump in 2020. By a margin of 47 percent to 28 percent they express a preference for a Democratic-controlled Congress.

What this group wants – and how many of them turn out to vote – could determine the makeup of Congress when Americans go to the polls in less than three weeks.

Eighteen years ago, RealClearPolitics pioneered the averaging of public opinion polls, a concept now generally accepted and widely practiced. Under Della Volpe’s direction, RealClear Opinion Research seeks to delve deeper into what informs Americans’ political views. It is not a horse race poll.

“Beyond traditional labels and parties, we were seeking to understand the nuanced values and culture that voters carry with them as we approach the midterms and beyond,” said Della Volpe, who is also the director of polling at the Harvard Kennedy School’s Institute of Politics. “We asked Americans to offer perspective on how well we are adhering to the core principles found in the preamble to the Constitution, the role of federalism, the images and declarations that unite and divide us all.”

Notwithstanding the binary ballot choices presented at election time or the relentless diet of stylized partisan sniping on cable news, the 2016 presidential election and its aftermath have revealed widespread dissatisfaction with the reigning two-party duopoly. Partly, that’s progress: The America governed by Thomas Jefferson -- the nation of Federalists and Republicans -- existed only on the Eastern Seaboard, at a time when slavery was legal in the Southern states, when women couldn’t vote, immigrants came primarily from Western Europe, and gay rights and gender politics were a long way from being public issues.

But if two political parties were adequate in that America, no 21st century U.S. president, even one who cared about trying to unite the country, could accurately say after Election Day, “We are all Republicans, we are all Democrats.” Political attitudes today are far more visceral and varied. That word “tribes,” which Della Volpe settled on, has struck numerous social scientists as a better description of the current climate.

The term has been employed by social commentator Andrew Sullivan, political writer Ron Brownstein, and MSNBC political correspondent Steve Kornacki, who writes in a recent book about the origins of our current “political tribalism.” An ambitious new study by a group of international academics who’ve coalesced under the rubric More in Common -- a group formed to foster stronger social bonds -- is called “Hidden Tribes: A Study of America’s Polarized Landscape.”

That study delineates seven “American Tribes.” The new RealClear Opinion Research poll identifies five, grouping them on the basis of a series of questions about voting behavior, political identification, stances on issues, and assorted attitudes about race, immigration, and other wedge issues. Survey respondents, for example,

were shown photographs ranging from U.S. Marines in combat and an American flag on a rural barn to NFL players kneeling and an interracial couple and their child. They were also asked to respond to a series of statements by modern U.S. presidents.

The Resistance (26 Percent)

Three out of four people in this category self-identify as Democrats, 85 percent of whom say they’d never vote to re-elect Trump -- which is no surprise. These motivated liberals aren’t necessarily waiting until 2020, either. More than 90 percent of them favor a Democratic takeover of the House and Senate, both to advance a liberal agenda on issues ranging from expanding health care and campaign finance reforms and, presumably, to jump-start congressional investigations of the president, possibly including impeachment.

The Resistance strongly believes that racial diversity in our country “makes us stronger,” that immigration is good for the country, and that NFL players taking a knee to protest during the national anthem shows “what’s right about America.”

Majorities of the Resistance do not share that view when shown photos of the American ﬂag on a barn, worshipers at church, U.S. Marines in combat, or even just a plain old truck driver. Thirty-six percent of this segment are under 45, while 58 percent are female and 55 percent white. Interestingly, this group is not dominated by left-wing ideologues: Support for a 2020 presidential bid by Joe Biden is nearly 20 points higher among this group than for the more left-leaning potential candidates, Sens. Bernie Sanders and Elizabeth Warren.

Nonetheless, if 26 percent of Americans can be categorized as being in this tribe, it suggests that the Resistance is the dominant wing of the Democratic Party – since only 40 percent of respondents identify themselves as Democrats.

Mainline GOP (14 Percent)

Heading into the 2018 midterms, the good news for the Republican Party is that this group remains deeply loyal, even if Trump was never their guy. Ninety-four percent of them want Congress to remain in Republican hands – and 82 percent “definitely” plan to vote in the midterms. The bad news? There just aren’t that many of them: Mainline GOPers make up only 14 percent of registered voters. This tribe is old (only 17 percent are under 45); heavily male (67 percent); very white (85 percent); well educated (37 percent have a college degree). Sixty-one percent of them live in suburbs.

They rate taxes as their most important issue, followed by religious freedom. When it comes to immigration and ethnic diversity, however, they neither follow Trump’s lead nor have much in common with his grassroots supporters. Asked, for example, whether they agree that “new, legal immigrants are good for the U.S.,” 74 percent of Mainline GOP tribe members strongly agreed. This is four times as high as the percentage of MAGAs.

Fifty-one percent of Mainline GOPers agree that “racial diversity should make us stronger,” compared to only 12 percent of MAGAs. On these kinds of questions, the Mainline GOP was closer to the Resistance than any other group. To pro-Trump populists, such findings confirm their belief that the Republican establishment isn’t appreciably different from the Democratic establishment. On the other hand, it undermines the prevailing narrative in the liberal media that Republicans are racists. The Mainline GOP tribe certainly isn’t.

MAGA (12 Percent)

Making America great again, in the minds of these hard-core Trump supporters, means keeping Congress under Republican control -- by a margin of 88 percent to 5 percent. Yet, only 65 percent say they definitely plan to vote in the midterms, significantly lower than Mainline GOPs.

Eight out of 10 indicate they they’d vote to re-elect the president in 2020. This group is younger than the establishment Republican tribe, with 25 percent being under 45. They are also less likely to have a college degree. Ninety percent of them are white, which will strike some liberals as low, and 54 percent of MAGAs are female. They are the most rural of any tribe, and are three times more likely than Mainline GOPers to agree with this statement: “The way capitalism in practiced in America today is broken.”

They have other attitudes in common with the Resistance, too. Mostly notably, MAGAs rate health care as their most important domestic policy issue – though their solutions to the issue likely differ. They also express less allegiance to the Republican Party than the Resistance does to the Democratic Party. Asked whether the GOP cares about “people like me,” only 54 percent answered affirmatively. When members of the Resistance were asked that question -- about the Democratic Party -- 69 percent of them said yes.

More than any other tribe, MAGAs concur with the statement: “I often feel under attack because of the color of my skin.” By more than a 2-1 margin they disagree that “racial diversity in our country should make us stronger” and are much less likely than any other group to believe legal immigration is good for the United States.

Independent Blues (24 Percent)

This group may lean toward the Democrats, but it is also the most likely (48 percent) to wish for “another political party” they could get behind. This tribe is not monolithic in terms of party loyalty: 37 percent are Democrats, 37 percent are independents, and 26 percent are Republican. Only 16 percent say there is a good chance they will vote to re-elect Trump in 2020.

Like their cousins in the Resistance, they prioritize health care, K-12 education and higher education as important policy issues, although unlike the Resistance they don’t see these primarily as federal issues. When read a quotation from Ronald Reagan’s first inaugural address (“In this present time, government is not the solution to our problem; government is the problem”), 64 percent of the Independent Blues concurred, putting them much closer to the pro-Trump tribe than the Democratic Party base.

The Independent Blues differ from the Resistance in other significant ways, too. They don’t rate abortion rights as very important, and they align more closely with the two pro-Trump tribes on some culture war questions. Two-thirds of the Independent Blues believe Americans have become “overly sensitive,” compared to just 24 percent of the Resistance. Shown images of the ﬂag and of churchgoers in the pew, about 60 percent say these scenes depict what’s “right” about America. On one issue, however, they are in sync with the Resistance. Shown a photo of a gun show, only 10 percent of them say that’s what is right about America.

Respondents were asked whether they agreed with following statement: "From this day forward, a new vision will govern our land. From this day forward, it's going to be only America first." This line from Trump's inaugural address served as a bedrock organizing principle of his 2016 campaign. Perhaps surprisingly, the Mainline GOP tribe voiced the most support for this "America First" mantra (79 percent) -- slightly higher than even the MAGA tribe. Not surprisingly, 69 percent of those in the Resistance disagreed with the statement. Independent Blues were split: 25 percent were in agreement while 31 percent disagreed.

The Detached (24 Percent)

Although 41 percent of this group reports listening to podcasts “at least” a few times each week, it’s not likely that they are tuning in to political programming: This group is the least likely to vote in the 2018 midterms. Although they supported Hillary Clinton over Donald Trump in 2016 by 14 points, their views about Trump’s party appear to have softened: Asked which party they’d like to control Congress, they favored Democrats, but only by a seven-point margin.

In terms of partisanship, this group is close to the national average. Thirty-eight percent say they are “sure to” or believe there is a “good chance” they’d vote for Trump in 2020. Perhaps because they are the youngest tribe – and the most likely to be employed – the Detached are less likely than other groups to rate health care as a “very important” issue. Then again, they don’t rate any public policy issue as important as the other groups did. The Detached just aren’t that into politics.

The Very Image(s) of a Fractured America

One takeaway from this study of the American electorate is how tribal symbols and totems show how divided we are. “When I look at the photos, I am struck by how the politics of division have changed how we view America and ourselves,” Della Volpe said. “My Irish and Italian grandparents would never have thought that images of the U.S. Marines or a flag on a barn, a truck driver, worshipers at church, or an athlete in a classroom have become predictors of which party you choose to support.”

Nonetheless, another conclusion that can be drawn for this data is that political professionals from both major parties, along with the new media, spend far too much time focusing on reactions from the far left and far right of American politics. Among those too often forgotten are those in the middle, the tribes we call the Detached and the Independent Blues -- fully half of America’s registered voters.

A generation ago, the Independent Blues were proud to be called “Reagan Democrats.” Today, they align with their country’s politics in more subtle ways. They agree with the Democratic Party on policy issues such as health care, education, and gun control, but are turned off by political correctness and identity politics. They honor the flag and respect religion. “Caught in the cross-fire of our culture wars that are tearing our country apart, they tend to be ignored,” said Della Volpe. “Yet they might very well choose our next president.”

Carl M. Cannon is the Washington Bureau Chief for RealClearPolitics. Reach him on Twitter @CarlCannon.

