f I asked you what most defines Donald Trump supporters, what would you say? They’re white? They’re poor? They’re uneducated? You’d be wrong. In fact, I’ve found a single statistically significant variable predicts whether a voter supports Trump—and it’s not race, income or education levels: It’s authoritarianism. That’s right, Trump’s electoral strength—and his staying power—have been buoyed, above all, by Americans with authoritarian inclinations. And because of the prevalence of authoritarians in the American electorate, among Democrats as well as Republicans, it’s very possible that Trump’s fan base will continue to grow. My finding is the result of a national...