WASHINGTON — The biggest impact of President Donald Trump’s vow to undo a law that limits political activities by churches and charities might not be about free speech but campaign finance, experts say.

Some say the move could create a backdoor way for big-money donors to anonymously pump millions of dollars into campaigns — while getting a tax deduction for doing it.

You’d see millions and millions of dollars going through charities to influence campaigns,” said Roger Colinvaux, an expert on tax law and nonprofits at the Catholic University of America in Washington. “For wealthy donors, it would be the gold standard: They’d get a tax deduction and anonymity.”

Others say the church should be allowed a vocal role in political issues.

“Historically, the church always had an influence on politics and issues of the day,” said the Rev. Jason McGuire of upstate Lima, who leads New Yorkers for Constitutional Freedoms, an evangelical-based non-tax-exempt group that weighs in on political issues in the Empire State. “The church has always been the conscience of the country.”

Trump, a Republican, recently repeated his campaign pledge to “totally destroy” the Johnson Amendment, a 1954 law intended to prevent religious and many other nonprofit entities from engaging in electioneering by threatening their tax-exempt status.

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The law, named for its author, then-Sen. Lyndon B. Johnson, came after decades of debate in Washington about the role of political activity in charitable contributions.

Contrary to widespread belief, the law wasn’t aimed specifically at churches or solely at Johnson’s efforts to silence a nonprofit that was calling him a Communist, said Miriam Galston, a George Washington University law professor.

“It had been on the table a very long time,” Galston said. “There had been congressional hearings ... It was not a vengeful thing Johnson did, but thought-out legislation.”

The law doesn’t actually prevent pastors, churches or other entities from speaking out, Galston said, adding that the limits on speech have been a bit “overstated.”

Religious leaders can advocate for a candidate (or an issue such as abortion, poverty or climate change) in their personal capacities, as long as they are careful not to speak for a church itself. A church or organization can get involved in campaigning and raising money — as long as it foregoes its tax-exempt status.

Trump’s declaration against the amendment was hailed by church leaders at the National Prayer Breakfast on Feb. 2. For the president’s allies, his words were the first step toward fulfilling a campaign pledge he made in a speech to evangelicals.

“I remember very vividly that one promise he made: repealing the Johnson Amendment,” said McGuire. “Most of the people in the group were Christians that are more actively engaged in political issues. They knew what the Johnson Amendment meant.”

When Trump said he’d push to abolish the law, “there was applause and cheers,” McGuire said. “There were people who jumped to their feet.”

Not all clergy members think the restriction on campaigning should be lifted.

“This opens up a can of worms that would undermine the church’s moral authority,” the Rev. Raphael Warnock, a Baptist pastor in Atlanta, told The Associated Press.

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There are two pending Republican-sponsored bills dealing with the Johnson Amendment, although it’s unclear how a Republican-controlled Congress ultimately will act.

Rep. Walter Jones Jr. (R-N.C.) introduced a bill that strikes the Johnson Amendment altogether

A contrasting bill, sponsored by Sen. James Lankford (R-Okla.) and Reps. Steve Scalise (R-La.) and Jody Hice (R-Ga.), would amend it to state that charitable organizations can “make statements relating to political campaigns if such statements are made in the ordinary course of carrying out its tax-exempt purpose.” Lawmakers would have to define what “ordinary course” means.

In a Feb. 6 Washington Post Op-Ed, the sponsors of the Lankford bill contended the Johnson Amendment is an unconstitutional muzzle on free-speech rights, and that changing the law won’t turn churches into “arms of political parties.”

“While our legislation is specifically drafted to maintain the prohibition against 501(c) (3) organizations contributing money to candidates or campaigns — that way taxpayers aren’t funding them — we also drafted it to stop the IRS from censoring their free-speech rights,” the Republicans wrote.

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The fallout of repeal would be multifaceted, analysts say.

Charities could come under pressure from donors to get involved in political campaigns. Longtime donors could become soured by the introduction of politics and stop giving to certain organizations. Thinly cloaked “charitable” organizations could be founded as a means of moving political money.

“It doesn’t take much imagination to see a donor who could offer hundreds of thousands of dollars, millions, whatever, to leverage the charity to do something not consistent with its mission, and I think that would be bad for the charity sector as a whole,” Colinvaux said.

“What else would happen is that you’d see a lot of new charities form — it’s easy to form a charity,” he said. “Groups will form them with partisan intent, dress them up with some charitable activities, and the IRS won’t be able to police it.”

Big money already saturates politics, through donations directly to candidates and to special-interest groups, but such contributions aren’t tax-deductible.

Opening such a lucrative way to fund campaigns “would really change the landscape,” with big money in politics going from political-action committees to political charities, Galston said.

“You’d hear the sound of money shifting,” she said.