Donald Trump has been accused of many things, but being convincingly religious is not one of them.

He claimed his favorite book is the Bible and even waved one around at a political rally, but was initially unable to name his favorite verse when asked. He has compared himself to altar-call evangelist Billy Graham, but also said he’s never asked God for forgiveness. He claimed to be a faithful Presbyterian, but then the church he claimed to attend released a statement saying he was not an “active member.”

Jerry Falwell Sr., by contrast, founded the Thomas Road Baptist Church at age 22 in 1956. When Falwell wanted to make a point, he didn’t just wave a Bible; he quoted extensively from the book he called “the infallible word of God.” While some would say he misinterpreted or misapplied its teachings to fit his political ends, none would accuse the preacher of being irreligious. (I heard many scripture-laden sermons from Falwell Senior when I was an undergraduate student at Liberty University from 2000 to 2004.)

The differences here are not inconsequential. A 2015 poll by the Barna Group found that evangelicals are far more concerned with a candidate’s faith than the general population. 45 percent of evangelicals say religious faith is one of the most important factors in choosing a presidential candidate, compared with only 9 percent of all Americans. If Trump can’t at least seem more devout than he has in the past, he can’t expect to shepherd more of the conservative faithful into his flock.

But the rift between Trump and evangelical stalwarts like Falwell has as much to do with politics as piety.

Conservative Christians tend to place a disproportionate amount of emphasis on a handful of issues—these days, abortion and LGBT issues. These are issues on which most have refused to compromise.

Falwell Senior was passionate about these two matters, perhaps to his peril. An outspoken pro-lifer who advocated the overturn of Roe v. Wade, the preacher pressed for the appointment of anti-abortion judges and for greater restrictions to abortion services at the state level. He stressed the need for “viable alternatives” to abortion. He even launched the “Liberty Godparent Home,” which helped facilitate adoptions for expectant mothers who wished to bring their children to term but could not care for them.

Though Trump now describes himself as pro-life, as late as 1999 he labeled himself “very pro-choice” on Meet the Press. He says his conversion on the matter is due to hearing personal stories of children who were nearly aborted, but the journey has not been a swing from one extreme to another. In an interview with Bloomberg News’s Mark Halperin in January of 2015, he said, “I’m pro-life, with the caveats. You have to have the caveats.” Trump listed the exceptions as incest, rape, and protecting the life of the mother.