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.
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.
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