The only group Donald Trump seems to like less than Mexicans is Muslims.

The presidential frontrunner incited controversy this week after he indicated to two reporters that he wouldn’t rule out setting up a national registry or special identification cards for Muslims. He went on to say that such a database would be feasible with “good management procedures” that would go “beyond databases” and would included “signing them up at different places,” not just mosques. The real-estate mogul later backed away from the idea, tweeting that a reporter, not him, first suggested a possible Muslim database.

The most amazing thing about Trump possibly-sort-of-maybe proposing a database for Muslims is that is doesn’t sound all that amazing. The idea falls in line with previous boorish comments about Muslims. But many of his supporters—especially the Christian ones—don’t seem to realize that supporting his proposals could actually backfire on them.

For those concerned about Donald Trump’s Muslim policies, the most telling moment might be his response to a questioner at a town hall meeting in Rochester, New Hampshire, this past September.

“We have a problem in this country. It’s called Muslims,” the questioner said.

“Right,” Trump replied.

“You know our current president is one,” the questioner, wearing a “Trump” T-shirt continued. “You know he’s not even an American.”

“We need this question,” Trump interrupted with a laugh. “This is the first question.”

"But anyway, we have training camps growing where they want to kill us,” the man, said. “That’s my question: When can we get rid of them?"

“We’re going to be looking at a lot of different things,” Trump replied. “You know, a lot of people are saying that and a lot of people are saying that bad things are happening. We’re going to be looking at that and many other things.”

Many were bewildered that Trump would even dignify such a question, much less seem open to the idea of getting rid of American Muslims. Those who were alarmed soon had more reason to feel anxious. Over the past several months Trump has continued to suggest that the United States should consider forcibly shutting down some mosques in order to fight terrorism. His support for the idea seems to oscillate between “strongly consider” and “absolutely no choice [except to close some mosques].”

“Nobody wants to say this and nobody wants to shut down religious institutions or anything, but you know, you understand it,” Trump told Fox News’s Sean Hannity. “A lot of people understand it. We’re going to have no choice.”

One might assume that Christians of the “Bible-believing” variety would be alarmed by such rhetoric. Trump’s proposals are eerily similar to passages in the Bible’s book of Revelation, which many Christians believe predict a future apocalypse.

Some Christians have let Revelation prophecies influence their political positions on issues such as climate change and supporting Israel. But the Bible also tells of oppressive government power that forces the registration and issuance of special forms of identification—a “mark,” which is used to discriminate against religious people in the marketplace and broader society. If Christians believe such a future is possible and coming, they might ask whether Trump’s support could become a gateway to it.

Many Christians, however, find Revelation’s predictions far-fetched or consider them allegorical. These believers can still look to the Old Testament book of Proverbs, which warns, “Whoever digs a pit will fall into it; if someone rolls a stone, it will roll back on them” or the New Testament book of Galatians, which similarly teaches that “A person harvests whatever he plants.”

Some conservative Christians look more to the Constitution than to the Bible for guidance on political matters. For them, the gaping problem with Trump’s proposals is that they run afoul of freedom of religion. In America, houses of worship enjoy special kinds of exemptions. They do not pay taxes on the money they collect or the land they own, and they have always been protected from government regulation and interference.

If a President Trump were to reverse that with respect to Muslims, perhaps with the tacit approval of the increasingly fearful American public, the potential ramifications for all religions could be disastrous. American religious freedom includes all houses of worship—mosques, synagogues, and Christian churches. While Trump’s current proposals only concern mosques, Christians or Jews or Buddhist could find themselves on the receiving end of that government stick at some future date.

Trump’s seeming willingness to target particular religious communities and consider closing houses of worship is George Orwell’s nightmare. But it should also be alarming to Christians who take the Constitution seriously. Russell Moore, the president of the Ethics and Religious Liberty Commission of the Southern Baptist Convention, got it right when he emphasized the dangers of such policies to Buzzfeed:

Donald Trump is saber-rattling about shutting down mosques in this country, which, as somebody who works every day on religious liberty, I’m astounded that we could have a presidential candidate of either party speaking in such a way. Evangelicals should recognize that any president who would call for shutting down houses of worship ... is the sort of political power that can ultimately shut down evangelical churches.

Trump’s supporters are mostly conservative and many are Christian. These two groups commonly claim that Christians are becoming a marginalized movement in American society. If they truly believe that American culture and government bodies are increasingly antagonistic to the Christian religion, they have many reasons to prefer that Donald Trump stay in his Manhattan tower and far away from 1600 Pennsylvania Avenue.

A threat to the freedom of any religion is a threat to them all.