Donald Trump has tended to fare worst in states that are mostly white.

That doesn’t mean he hasn’t had great success in appealing to white Republican primary voters — there’s no doubt of that — only that he generally does better in states that have higher percentages of nonwhites, particularly African-Americans.

Mr. Trump’s stances on, say, trade and Social Security can strike a chord with voters. But studies have shown that his bigger appeal is as an authoritarian voice of the voiceless. Part of that has been rallying people — particularly those who haven’t gone to college — who feel a resentment toward racial, ethnic and religious “others.”

As Michael Tesler and John Sides wrote for the Monkey Cage at The Washington Post last week: “Fifty years of research backs this up. Ethnocentric suspicions of minority groups in general, and attitudes about blacks in particular, influence whites’ opinions about many issues.”

Some social science research suggests that the simple fact that President Obama is black might have contributed to a sense of lost power and resentment among whites, and, of course, Mr. Trump first came to political prominence by questioning whether Mr. Obama was even a citizen.