With Nikki Haley set to mount a last stand of sorts in the South Carolina primary later this month, there’s a hidden reason that Donald Trump has been so dominant throughout the GOP nomination process: White evangelicals. Their support for Trump has held through impeachments, scandals, revelations about sexual assault, multiple serious criminal prosecutions, and even a coup attempt. We talked to Sarah Posner, a scholar of the religious right, about what explains Trump’s extraordinary hold on these voters—and why it’s changing the Republican Party in insidious, alarming ways.