President Trump, speaking at the National Prayer Breakfast, promised to "get rid of and totally destroy the Johnson Amendment," which prohibits some tax-exempt organizations like churches from supporting political candidates, on Feb. 2. (The Washington Post)

A version of this story was first posted on Feb. 2, 2017. It has been updated.

President Trump is expected to sign an executive order on Thursday relaxing rules that bar tax-exempt churches from participating in politics.

The move, which is part of a broader step on religious liberty, aims to fulfill a promise Trump made repeatedly during his campaign that he would do away with something known as the Johnson Amendment. In his address at the National Prayer Breakfast on Feb. 2, he vowed again, “I will get rid of and totally destroy the Johnson Amendment.”

What is that? Is it in Trump’s power to destroy it? And who would want him to do that?

What the Johnson Amendment is: It’s named for Lyndon B. Johnson, who introduced it in the Senate in 1954, nine years before he became president. It bans all tax-exempt nonprofits — which includes churches and other houses of worship, as well as charities — from “directly or indirectly” participating in any political candidate’s campaign.

President Trump has vowed to repeal the Johnson Amendment, because he says it infringes on the freedom of speech of religious groups. Here is what you need to know about this amendment. (Bastien Inzaurralde/The Washington Post)

What Trump can do: Trump presented the ban on participating in politicking as a restriction on the freedom of faith groups to put their religion in action, if their religion calls on them to campaign for a candidate. The Johnson Amendment is part of the tax code, so to completely remove it would take an act of Congress.

“If he ‘totally destroys’ the Johnson Amendment, he will way overreach and open an enormous loophole,” said Douglas Laycock, professor at University of Virginia Law School and an expert on religious freedom who has urged Congress to fix the amendment. What Trump could do, however, is direct law enforcement discretion elsewhere or maybe say it’s unconstitutional.

The next president could direct the IRS to enforce it, for example, but churches would be free from worry about their political speech or donations during Trump’s term.

How it actually works: Most of the discussion of the Johnson Amendment, whether coming from Trump or from pastors, focuses on whether clergy put their churches’ tax-exempt status at risk when they endorse their favorite candidates from the pulpit.

But in reality, the Internal Revenue Service very rarely punishes churches for political statements. For several years, more than 2,000 pastors have joined what they call “Pulpit Freedom Sunday” to test the ban by speaking their political views in their sermons — and the IRS investigated one and did not punish in that case, according to the conservative organization that organizes the annual effort. In the 1990s, a church called Branch Ministries lost its tax-exempt status after taking out a full-page ad against President Bill Clinton in USA Today.

But the Johnson Amendment has not been at the forefront of the debate about religious liberty, which has in recent years been centered around contraceptive access and LGBT rights.

“In the universe of religious freedom issues facing our country today, the Johnson Amendment doesn’t come even close to the top,” said John Inazu, professor of religion and law at Washington University in St. Louis. “My hunch is that one or two of Trump’s ‘religious advisers’ mentioned the Johnson Amendment early in the campaign. But how and why they focused on that issue is beyond me.”

What Trump hasn’t talked about in his speeches about the Johnson Amendment is the implication for how churches can spend their money, not just how clergy can talk about candidates.

“Most people’s concern is if you allow churches to freely allow political activity — churches, synagogues, temples, whatever the religious organization — now what you’ve done is you’ve turned those into Super PACs,” said David Herzig, a Valparaiso University tax law professor.

Churches would be freed to use their budgets to support campaigning — and citizens would get a tax deduction for contributing to the church, which would still be a 501(c)3 nonprofit. Also, Herzig pointed out, nonprofits like churches aren’t required to make the same public disclosures as PACs, so political funding could theoretically become much less transparent if campaign funding were funneled through churches.

Some critics are worried doing away with the amendment could allow a huge flow of money in campaigning between churches and candidates. But, Herzig says, even without the Johnson Amendment, the country’s tax law severely constrains churches’ ability to engage in politics.

Who wants it gone: Until Trump’s campaign, the Johnson Amendment rarely came up in political discussion. Some pastors, including those 2,000 who publicly oppose the policy on Pulpit Freedom Sunday, objected to the ban, but it wasn’t high on most Christians’ policy wish list.

LifeWay, a Christian polling firm, found in 2015 that 79 percent of Americans thought clergy should not endorse candidates during worship services. Evangelicals were more likely to say pastors should be able to do so — 25 percent compared to 16 percent — but support for clergy endorsements was low across the board.

Trump’s attack on the Johnson Amendment has found eager supporters, though, including Jerry Falwell, Jr., president of Liberty University, and other prominent evangelicals who supported his presidential campaign.

Falwell said on Wednesday that Liberty officials have been “harassed” by organizations that would report the university for violating the Johnson Amendment.

“I don’t think it was being enforced anyhow, but it had a chilling effect on pastors and conservative universities,” Falwell said.

On the other hand, many religious groups like their nonpolitical status just fine the way it is.

Interfaith Alliance president Rabbi Jack Moline said on Wednesday that the Johnson Amendment has prevented houses of worship from being turned into partisan political tools.

“To hear the Religious Right say it, clergy in America are being muzzled. But that’s a lie,” he said in a statement. “Repealing the Johnson Amendment is nothing more than President Trump carrying water for the Religious Right.”

According a 2016 survey the Pew Research Center, about 10 percent of parishioners say they have heard direct support for or opposition to a specific candidate. Among those who heard religious leaders speak out for a candidate, Hillary Clinton was the name mentioned most often, with 6 percent of recent churchgoers saying their clergy had spoken out in support of her. Black Protestants were much more likely to say they had heard their clergy speak out directly about specific political candidates, according to Pew.