But despite the improved attitudes, Muslims remain the least popular of all religious groups asked about in the Pew survey. By comparison, respondents gave Jews a rating of 67, Catholics 66, and mainline Protestants 65. Even atheists were rated higher at 50.

Data in the figure below from the 2016 pilot study of the American National Election Studies (ANES) show the same thing. On a feeling thermometer, Muslims are ranked near the bottom compared with other groups in the United States — including blacks, Latinos, transgender people and gays and lesbians — and below the neutral point of 50.

What explains this deep prejudice toward Muslims?

One reason is ethnocentrism

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My research shows that ethnocentrism — generalized dislike toward all out-groups — plays a key role in determining people’s attitudes toward Muslims. Those who feel cold toward blacks, Latinos, Jews, homosexuals, feminists and other minority groups also feel cold toward Muslims. In other words, anti-Muslim prejudice is strongly related to racism, antigay attitudes, sexism and anti-Semitism. This suggests that there is a general psychological tendency at work in understanding prejudice toward Muslims.

Strong empirical support for this theory shows up in the 2016 ANES pilot study. For instance, a general measure of ethnocentrism — based on attitudes toward blacks, Latinos, homosexuals, feminists and transgender people — strongly predicts people’s feelings about Muslims. People who are the most ethnocentric give Muslims on average a rating of 24 on a feeling thermometer, while those who are least ethnocentric rate Muslims at 67. This gap is similar when I use an alternative ethnocentrism measure developed by Cindy Kam and Donald Kinder.

Another reason is, increasingly, partisanship

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But a second factor has been gaining importance in explaining anti-Muslim prejudice: partisanship. Although my earlier research established that party identification and ideology were not associated with attitudes toward Muslims, that is no longer true.

In the 2016 ANES, for instance, Democrats give Muslims an average rating of 55, while Republicans rate them 32. In 2004, the difference was less than 10 points; on average, Democrats rated Muslims at 57 points whereas Republicans rated them at 51 points.

Why are attitudes toward Muslims increasingly so different along partisan lines? One explanation is elite rhetoric.

After the Sept. 11, 2001, attacks, George W. Bush emphasized separating terrorists from the peaceful religion of Islam. That’s no longer the attitude of some Republican leaders, who now make explicitly prejudiced statements about Muslims.

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For instance, during the presidential campaign, Donald Trump proposed banning Muslims from entering the United States, much as he made negative statements toward other racial and ethnic minority groups. Ben Carson, former presidential nominee and current secretary of housing and urban development, many times explained why he would not support a Muslim for president, and how basic tenets of Islam are in conflict with the U.S. Constitution.

Political science research has shown that such elite cues have tremendous power in influencing followers. Such statements therefore almost surely help explain the wide partisan differences in attitudes toward Islam.

Finally, dislike is reinforced by a generally negative cultural portrayal of Muslims

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But the broader cultural environment matters as well. Opinion leaders, pundits and the media often depict Muslims negatively. Work in progress also suggests that negative media portrayal influences attitudes toward Muslims.

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Of course, it’s also possible that people who are already prejudiced toward Muslims tend to seek out these news outlets as their primary sources of information, reinforcing their inclinations. These studies largely fail to rule out this possibility.

Meanwhile, anti-Muslim attitudes are rarely counterbalanced by positive portrayals. This summer, after Trump attacked the parents of a U.S. Muslim soldier who was killed in action, for speaking at the Democratic convention, support swelled briefly for the Khan family — a moment notable in part because it was so unusual. What’s more, that too was in a partisan frame.

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Some evidence suggests that even a slightly more positive portrayal of Muslims may substantially change attitudes. For example, a recent experimental study by Democracy Fund Voice finds that positive portrayals of Muslims can dramatically improve attitudes among Republicans, particularly those who do not support Trump. In the study, some respondents see a YouTube video with Muslim Americans, calling themselves American-born and raised, reading and reacting to cruel Facebook comments about a mosque that was burned down in Florida. A majority of non-Trump GOP supporters had grown a favorable attitude toward Muslims after this treatment. After the video, some strong Trump supporters also expressed more positive feelings toward Muslims.

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But of all the factors examined in a model, ethnocentrism is still the strongest predictor of how people feel toward Muslims. Next comes partisanship. Anti-Muslim prejudice still goes hand-in-hand with racism, anti-Semitism and sexism with a slight partisan tone. All that is reinforced by the media and elites’ ongoing disdain toward Muslims, which keeps that group at the bottom of the social hierarchy in most Americans’ minds.