Mr. Jeffress’s expression of acute vulnerability is key to understanding white evangelical support for Mr. Trump and the extraordinary lengths to which evangelical leaders are going so they can rally behind him. Leaders like Mr. Jeffress locate the threats to their security in the larger world around them.

But the anger, anxiety and insecurity many contemporary white evangelicals feel are better understood as a response to an internal identity crisis precipitated by the recent demise of “white Christian America,” the cultural and institutional world built primarily by white Protestants that dominated American culture until the last decade.

Today, white evangelicals are not only experiencing the shrinking of their own ranks, but they are also confronting larger, genuinely new demographic and cultural realities. When Barack Obama was elected president in 2008, white Christians (Catholics and Protestants) constituted a majority (54 percent) of the country; today, that number has slipped to 45 percent. Over this same period, support for gay marriage — a key issue for evangelicals — moved from only four in 10 to solid majority territory, and the Supreme Court cleared the way for gay and lesbian couples to marry in all 50 states. The Supreme Court itself symbolized these changes, losing its last remaining Protestant justice, John Paul Stevens, in 2010.

A recent Public Religion Research Institute-Brookings survey shows the alarm that white evangelical Protestants are feeling in the wake of demographic and cultural changes. Nearly two-thirds are bothered when they encounter immigrants who speak little English. More than two-thirds believe that discrimination against whites has become as big a problem as discrimination against other groups. For discrimination against Christians, that number is nearly eight in 10. And perhaps most telling of all, seven in 10 white evangelical Protestants say the country has changed for the worse since the 1950s.

By most measures, Ted Cruz, the son of an evangelical pastor and himself a Southern Baptist, should have been the evangelicals’ presidential candidate in 2016. But Mr. Trump won evangelicals over by explicitly addressing their deeper sense of loss. Mr. Cruz assured evangelicals that he’d secure them exemptions from the new realities, while Mr. Trump promised to reinstate their central place in the country. Mr. Cruz offered to negotiate a respectable retreat strategy, while Mr. Trump vowed to turn back the clock.