Donald Trump, no doubt, is the most confounding candidate produced by the American political system in decades. He offers enormous tax cuts, as any bona fide Republican candidate must. But he also wants to leave Social Security “as it is.”

He says he hates Obamacare, but offers “concepts of Medicare” to care for “people that can’t take care of themselves.” He has gutted the standard Republican position that favors freer trade.

The most surprising aspect about Mr. Trump’s solid appeal among Republican primary voters, though, may be what it says about the waning place of religion in American politics and the revival of a populism centered more on economic nationalism and white working-class discontent.

“It is intriguing that we have some notable challenges to the political establishment that are not coming from a traditional American religious place but from a surprisingly secular tradition,” said David Voas, head of the social science department at University College London.