“Utah exists today because foreign countries refused to grant the wishes of a misguided president and his secretary of state,” Herbert wrote in a Facebook post responding to Trump’s proposal. “I am the governor of a state that was settled by religious exiles who withstood persecution after persecution, including an extermination order from another state's governor. In Utah, the First Amendment still matters. That will not change so long as I remain governor.”

Trump, for his part, has tried harder to appeal to Mormon sensibilities since invoking his Muslim ban, launching a series of attacks on opponents that cast them as somehow un-Mormon. Last Friday, the Republican front-runner tweeted disparaging remarks about Senator Ted Cruz. Trump, who claims to be Presbyterian, said Cruz “should not be allowed to win” Tuesday’s Utah caucus because his views are out-of-step with the roughly 60 percent of the state’s population that identifies as Mormon.

“Mormons don't like LIARS!” Trump tweeted.

Hours later, Trump questioned the Mormon piety of Mitt Romney, the former Massachusetts governor and two-time GOP presidential candidate who also happens to be a devout member of the Church of Jesus Christ of Latter-day Saints (LDS). Romney, who won a whopping 93 percent of the vote in the 2012 Utah caucus, came out against Trump early March, calling him “a phony, a fraud.”

“Do I love the Mormons? I have many friends that live in Salt Lake City—and by the way, Mitt Romney is not one of them,” Trump told the crowd at a rally. “Are you sure he's a Mormon? Are we sure?”

Trump later claimed he was joking, insisting his point was that Mormons are “a very smart people” who should ignore Romney and back him in the Utah caucus, where 40 coveted delegates are at stake. But The Donald’s famously unshakable confidence—which has won him scores of evangelical Christian voters across the country—belies his consistently dismal support among Mormons. In fact, Mormon views of Trump are so toxic that he runs the risk of damaging the GOP’s longstanding lock on LDS members, who currently constitute the most reliably Republican religious group in the United States.

Trump, for instance, drew 11 percent support in the Beehive State in one recent poll—a distant third behind Senator Ted Cruz (53 percent) and Ohio Governor John Kasich (29 percent). And as BuzzFeed’s McKay Coppins points out, Trump has noticeably struggled to accrue Mormon votes throughout the 2016 election season, losing heavily Mormon counties during the primaries in Idaho and Wyoming—states where he placed second and third overall, respectively. In Oneida County in southeastern Idaho, where roughly 3 out of 4 voters are Mormon, Trump won just 17.8 percent of the vote, whereas Cruz walked away with 59.9 percent.

So what explains Mormon distaste for Trump? Some of it could be cultural, such as how Trump’s proclivity for insults and foul language contrasts sharply with the LDS church’s formal opposition to “any type of unclean or vulgar speech or behavior.” Some of it could be demographics; According to The New York Times, whites without high school diplomas are particularly likely to back Trump, but Mormons are significantly more likely than the general population to have at least some college-level schooling, with only 9 percent claiming less than a high-school education.