Why are white evangelicals supporting Trump? It goes back to Jimmy Carter.

Donald Trump’s first major rally of the 2016 campaign takes place Friday night in the heart of the Bible Belt. It’s not a natural fit for the often-crude, always-immodest New Yorker. But Trumpmania has even found its way to Mobile, Ala.

Organizers initially planned to hold the event at the town’s civic center, which can accommodate about 4,000 people. But after overwhelming interest — the Trump campaign says it has distributed more than 35,000 tickets so far — the rally was relocated to the 43,000-seat Ladd-Peebles Stadium. If it’s jarring to imagine Trump in a setting akin to a Billy Graham crusade, well, that’s just one more way in which the 2016 campaign is confounding conventional political wisdom.

Ever since a mid-July Washington Post poll confirmed that Trump is the leading candidate among white evangelical Republicans (20 percent supported him at the time, compared to 14, 12 and 11 percent for Scott Walker, Mike Huckabee and Jeb Bush, respectively), political observers have been trying to sort out the puzzle of conservative evangelical support for Trump.

This is, after all, a man who told the Iowa Family Forum that he can’t recall ever asking God for forgiveness (“I don’t bring God into that picture — I don’t.”) In a 2011 interview for the Christian Broadcasting Network, Trump characterized his church attendance as “always on Christmas, always on Easter, always when there’s a major occasion.” The Bible contains dozens of verses warning against the sins of pride and hubris and condemning those who exalt themselves — and Donald Trump is … Trump.

Trump’s unorthodox Christianity — not to mention his fairly liberal record of statements on social issues — seems to trouble evangelical elites, if not ordinary voters. In a World magazine survey of 100 prominent evangelical leaders, only three respondents named Trump as their preferred candidate. (Marco Rubio was the top choice, with 18 votes, followed by a tie between Walker, Cruz and Bush.) The Southern Baptist Convention’s Russell Moore has raised concerns over Trump’s immigration comments, telling reporters that “Mexican immigrants are far more likely to be Bible-believing Christians than to be criminals.” And some academics have tried to argue that many of those evangelicals backing Trump aren’t really evangelicals.

But while it’s easy to chuckle at the idea of Bible Belt voters rallying for a thrice-married real estate mogul who would never dream of turning the other cheek, Trump’s evangelical backing may not be that surprising. It’s been a long time since the personal morality of a candidate was a deal breaker for evangelical Republicans. They only reluctantly backed squeaky-clean Mitt Romney in 2012 as the GOP nominee, and yet voiced few concerns in 2008 when the divorced John McCain self-identified as a Baptist who has never been baptized.

Then-Democratic presidential nominee Jimmy Carter shakes hands with churchgoers in Plains, Ga., in 1976.  (Photo: AP)

In fact, conservative evangelicals have been disillusioned twice in the modern political era by evangelical presidents they originally backed. In 1976, which Time declared “The Year of the Evangelical,” the Southern Baptist Jimmy Carter brought millions of evangelicals into the political process — on behalf of the Democratic ticket. The list of white evangelicals who supported Carter that year reads like a who’s who of the religious right, including Pat Robertson, Jerry Falwell and Billy Graham. That fall, Carter won nearly half the evangelical vote. No Democrat has even come close in the decades since.

Once Carter moved into the White House, however, conservative evangelicals discovered that not all evangelicals are alike. They had assumed that shared religious beliefs would translate into shared political priorities. But Carter refused to support a constitutional ban on abortion and appointed no evangelicals to top posts in his administration. Worse, he pushed for ratification of the Equal Rights Amendment (the same-sex marriage battle of its day), and supported ending legal and cultural discrimination against gays and lesbians. By 1980, conservative evangelicals were ready to ditch one of their own for a divorced former actor who promised to be their culture warrior.

The conservative evangelical infatuation with George W. Bush lasted longer. But his second term — won, many evangelicals believed, on the strength of their turnout in the 2004 election — left many feeling betrayed. They believed Bush had indicated he would use his political capital to vigorously support a federal amendment banning gay marriage. When he instead put all of his effort behind a proposal to restructure Social Security, conservative evangelicals concluded they had been duped.

That disillusionment may explain as well as anything the difficulty Jeb Bush has had attracting support from evangelical Republicans. In that same July Washington Post poll, one-third of white evangelical Republicans expressed concern that Bush is too liberal. Only 15 percent said the same of Rubio — and of Trump.

Donald Trump’s unorthodox Christianity, not to mention his fairly liberal record of statements on social issues, seems to trouble evangelical elites, if not ordinary voters. (Photo: Brian Snyder/Reuters)

But what of Trump’s previous support for abortion, and liberal statements about gay rights? It may be that Republican primary voters simply don’t know much yet about Trump’s record. Or it may be that they simply don’t care.

After eight years of a Democratic president, Republicans want someone who can win, and they are especially eager to embrace a candidate who stands up for them. And while evangelical Republicans sometimes have different priorities and values than their non-evangelical peers, this could be an election cycle in which they vote as Republicans first and evangelicals second. In the same way, it was hard to identify specific motivations for Catholic voters in 2008 — exit polls showed that Catholics who voted for Obama were concerned about the economy and jobs, just like voters in general.

If Donald Trump’s momentum continues, it will be in large part because evangelicals decided they would rather hear a Yankee showman preach outrage than one of their own sing from the same old hymnal.