Donald Trump has now disavowed the support of white supremacist David Duke, shown here in New Orleans in 1978. (AP/Jack Thornell)

Donald Trump appeared to change his position twice over the weekend regarding David Duke, the notorious former grand wizard of the Ku Klux Klan who said he supports the candidate on his radio program last week.

Duke said he wasn't formally endorsing the candidate, but he encouraged his followers to volunteer for Trump's campaign, telling them, "You're going to meet people who are going to have the same kind of mindset that you have."

After being endorsed by Gov. Chris Christie (R-N.J.), Republican presidential candidate Donald Trump said on Friday, Feb. 26, that he disavowed former Ku Klux Klan leader David Duke's support. (Reuters)

On Friday, Trump denounced Duke during a news conference, only to tell CNN two days later that he didn't know enough about the white supremacist to condemn him.

"I don’t know anything about what you’re even talking about with white supremacy or white supremacists," Trump told the network's Jake Tapper.

By Monday morning, Trump had reversed himself again, disavowing Duke's support and saying on NBC's "Today" that he couldn't understand Tapper's question due to a faulty earpiece. Nonetheless, the episode provided further evidence that racism is a factor in Trump's success so far in the GOP presidential primary.

Trump's supporters appear to have little in common. He is the most popular candidate among all kinds of demographic groups in the GOP electorate. He wins with Republicans who are well educated and poorly educated, with religious as well as secular voters, with the rich and the poor, and with voters who see themselves as conservative and those who call themselves moderate.

While polling suggests that Trump's supporters have a variety of motivations, recent research suggests that prejudice, along with the trait psychologists call "authoritarianism," distinguishes many of those casting ballots for Trump from other Republican voters.

While choices about child-rearing might seem to have little to do with politics, polling shows Trump's supporters are more likely to value respect for authority and obedience in children, as Wonkblog has reported. Researchers say these views indicate authoritarianism, and indeed, Trump's supporters also are more likely than his rivals' supporters to believe the next president should suppress political dissent. Over the weekend, Trump also called for libel laws to be weakened to make it more difficult for the media to criticize him.

Authoritarianism is also associated with racial and ethnic prejudice. "They don't trust other people," Marc Hetherington, a political scientist at Vanderbilt University, said about authoritarians in a recent interview. "They're wary, and that's why they don’t want people who are different from them in the country, and don't think so highly of people who are from different races."

Opposition to immigration has been a crucial theme of Trump's campaign, which he announced last year by declaring Mexican immigrants criminals and "rapists." Polling by The Washington Post and ABC News shows that a majority of GOP voters who believe strongly that immigrants weaken  American society support Trump.

While some of these voters might hold that view due to economic concerns rather than xenophobia, recent research suggests that racism is part of what motivates opposition to immigration. As Wonkblog has reported, a recent experiment showed that white participants were less amenable to living and working alongside immigrants when shown a manipulated photograph of foreigners with darker complexions.

There are other reasons for Trump's appeal, to be sure. He is the most popular candidate even among voters who believe that immigrants strengthen American society, according to the the Post-ABC poll, though by a narrow margin.

Taken together, however, these findings suggest a possible explanation for Trump's unexpected success in the GOP primary. Instead of relying on the established factions of Republican voters that have selected presidential nominees in recent elections, Trump is instead creating a new coalition, exploiting some voters' racial and ethnic biases.

More from The Washington Post:

How America's dying white supremacist movement is seizing on Donald Trump’s appeal

Donald Trump loves the 'poorly educated' -- and just about everyone else

What social science tells us about racism in the Republican party