Republicans have long been the party of racial conservatism. Since at least the 1960s, the GOP's policies, rhetoric, and voters have been less supportive of minorities than have the Democrats'. These partisan differences over race have become especially pronounced during the Obama presidency.
But while white Republicans are more likely than white Democrats to express racially resentful beliefs, racial prejudice is thought to play a larger role in shaping the political preferences of liberals. In other words, racial politics has divided the Democratic Party's diverse coalition more than it has splintered the overwhelmingly white Republican Party.
Those historical differences have also been present in the two parties' presidential primaries. Vote choice in the 1984, 1988, 2008 and 2016 Democratic nominations, for example, were all sharply divided by race.
The Republican Party, however, has been more unified in recent decades around a "color-blind policy alliance," which calls for a diminished role of race in public policies. With the notable exception of Pat Buchanan's campaigns to preserve white cultural hegemony in the 1990s, few Republican candidates for president have attempted to directly distinguish themselves from their GOP rivals on matters of race and ethnicity.
Donald Trump's presidential campaign effectively bucked what the political scientists Donald Kinder and Lynn Sanders adroitly termed the Republican Party's electoral temptation of race — using implicit racial appeals to win over racially conservative voters without appearing overtly racist. Trump's play instead was to make several explicitly hostile statements about minority groups.
Trump has been willing to go where most Republican presidential candidates haven't. That might have made anti-minority sentiments a more potent force in the 2016 GOP primaries than in primaries past. That's plausible, because campaign appeals to racial and ethnic anxieties have often succeeded in activating support for politicians.
And that's exactly what the results below show.
In the first graph, I draw on data from the 2008 Cooperative Campaign Analysis Project (CCAP) and the 2012 CCAP, along with two combined YouGov surveys that were conducted in January and June 2016. The chart compares the relationship between racial resentment and support for the eventual Republican nominee among Republicans (including independent-leaning Republicans). Racial resentment measures beliefs that race-based inequality is due to cultural deficiencies in African American communities with statements like: "Blacks could be just as well off as whites if they only tried harder."
Consistent with a number of other studies, the chart shows a strong relationship between anti-black attitudes and support for Trump. Republicans who scored highest on racial resentment were about 30 percentage points more likely to support Trump than their more moderate counterparts in the bottom quartile of the party in racial conservatism.
That pattern is noticeably different from 2008 and 2012, when racial conservatism had a slightly negative relationship with support for the eventual GOP nominees. The upshot is that Trump was significantly more popular among the most racially resentful Republican voters than were his immediate predecessors, John McCain and Mitt Romney.
A similar pattern emerges in the next graph, which considers attitudes about Muslims. Republicans with very unfavorable views of Muslims were substantially more likely than their fellow partisans to support Trump in both RAND's Presidential Election Panel Survey and the 2016 American National Election Study Pilot Survey.
Attitudes toward Muslims were not a factor in the 2008 and 2012 Republican primaries. It appears, then, that Trump's hostile policies and rhetoric regarding Islam helped make him much more popular than prior nominees among the roughly 30 percent of Republicans who have a very unfavorable opinion of Muslims.
Along with Trump's proposed ban on Muslims entering the country, his hawkish immigration positions of mass deportation, ending birthright citizenship, and making Mexico pay for a border wall provide perhaps his strongest contrast with prior GOP nominees. In that light, it's not surprising that he performed much better than Romney and McCain with the substantial majority of Republicans (63 percent in the YouGov surveys) who want to deport unauthorized immigrants. That's depicted in the graph below.
To be sure, Trump is not the first presidential candidate whose support in the primaries was fueled by opposition to immigration. Buchanan, whose nativist presidential campaigns are frequently compared to Trump's, also performed well among anti-immigrant Republicans.
The results below from a CBS/NYT poll conducted immediately after Buchanan won the 1996 New Hampshire primary show him polling even with the eventual nominee, Bob Dole, among GOP voters who said that immigrants take jobs from U.S. citizens and that the country cannot afford to open its doors to any more newcomers.
But less than one-fifth of Republican voters agreed with both statements in the 1996 survey. That percentage would almost certainly be higher today, as Republicans have become more racially resentful and more opposed to immigration in the past 20 years.
The party's growing conservatism on matters of race and ethnicity provided fertile ground for Trump's racial and ethnic appeals to resonate in the primaries. So much so, in fact, that Donald Trump is the first Republican in modern times to win the party's presidential nomination on anti-minority sentiments.
Michael Tesler is associate professor of political science at University of California at Irvine and author of "Post-Racial or Most-Racial? Race and Politics in the Obama Era."