Congressional Republicans who have long disputed Democratic assertions that President Trump strong-armed Ukraine to help himself politically are pivoting hard to a new argument: The president’s actions are not impeachable — even if he did leverage his office for an investigation of a domestic rival.

For months, Trump’s allies on Capitol Hill have argued that Democrats are relying on secondhand information to support their allegations that Trump withheld military aid and a White House meeting with Ukrainian President Volodymyr Zelensky to pressure Ukraine to investigate his political rivals, including former vice president and 2020 candidate Joe Biden. Many Republicans have repeated Trump’s “no quid pro quo!” talking point.

But in his forthcoming book, former national security adviser John Bolton said Trump tied aid to a desired probe of Biden and his son Hunter, prompting Republicans to quickly change their message: On Tuesday, they latched on to an argument from Trump defense attorney Alan Dershowitz, that his actions don’t rise to the level of impeachment, even if the allegation is true.

“Let’s say it’s true, okay? Dershowitz last night explained that if you’re looking at it from a constitutional point of view, that that is not something that is impeachable,” Sen. Mike Braun (R-Ind.) told reporters Tuesday morning.

“Alan Dershowitz said it was not” impeachable, said Sen. Roy Blunt (R-Mo.), a top ally of Senate Majority Leader Mitch McConnell (R-Ky.). “And I don’t disagree with that.”

The ramifications are striking and could have long-term implications. The argument suggests senators believe a U.S. president can use taxpayer dollars to pressure an ally to investigate an American citizen who happens to be challenging him for president, without any repercussions. That was the basis of the House’s Dec. 18 impeachment charges, abuse of power and obstruction of Congress.

Most Republicans have also refused to say publicly whether they believe Trump’s actions were appropriate, with some growing angry when reporters press them for an answer.

But the new talking point also stands in stark contrast to a key argument by Trump’s most ardent defenders in Congress and his own legal team: that a quid pro quo never happened. As recently as Tuesday, Trump’s defense team was calling into question the notion that the president pressured Ukraine for a probe at all.

“The person that would be on the other end of the quid pro quo, if it existed, would have been President Zelensky,” said Trump’s attorney Jay Sekulow. “But President Zelensky — and we already laid out the other officials from Ukraine — have repeatedly said there was no pressure. . . . We are clear in our position that there was no quid pro quo.”

The diverging messages underscore the challenge Republicans face as they try to coalesce around an argument for why they don’t want to hear from witnesses after the White House stonewalled Congress. McConnell indicated in a closed-door meeting with Senate Republicans on Tuesday that he did not yet have enough votes to defeat an effort, expected later this week, to call additional witnesses and evidence in the trial.

Senators on Monday had been struggling to come up with an answer for why they don’t want to hear from Bolton. By Tuesday morning, they had found their answer in Dershowitz’s legal argument: If the allegation at hand isn’t impeachable, why ask to hear more?

The idea of acknowledging a quid pro quo first surfaced in the Senate this past fall, as more than a dozen current and former Trump administration officials testified to House impeachment investigators that they believed a White House meeting and $391 million in congressionally appropriated money were being withheld to pressure Ukraine. Sen. Ted Cruz (R-Tex.) told his colleagues in a private late-October meeting that by admitting the act occurred, Republicans could then argue that Trump did not have criminal intent, or perhaps that he even had a legitimate reason to ask for those probes.

But such a strategy contradicted Trump, who said he did nothing wrong, called his July 25 phone call with Zelensky “perfect” and denied that he tried to force a U.S. ally into announcing investigations of the Bidens. Indeed, Trump’s top House defenders, including Reps. Jim Jordan (R-Ohio) and Mark Meadows (R-N.C.), pushed back on any attempts by senators to simply acknowledge a quid pro quo happened and explain why.

The Republican argument, instead, was to deny a quid pro quo occurred. House Republicans said none of the Democrats’ witnesses had heard from Trump that he was directing the plan; even Ambassador to the European Union Gordon Sondland, who testified that it was clear there was a quid pro quo, couldn’t say who told him it was occurring.

Now, however, news that Bolton personally spoke with Trump about his intention to freeze military aid until he got an investigation has upended the GOP line that no “firsthand” witnesses have come forward. It sent Republicans into a private frenzy Monday morning, as some GOP lawmakers struggled with a sense of duty to call in Bolton to testify.

Enter Dershowitz, a Trump lawyer and emeritus Harvard law professor who argued Monday that “nothing in the Bolton revelations, even if true, would rise to the level of an abusive power or an impeachable offense.”

Lawyers and academics strongly disagreed with Dershowitz. Frank O. Bowman, a University of Missouri law professor and author of the book “High Crimes and Misdemeanors,” said Dershowitz’s view is out of step with mainstream constitutional scholars and historians.

“In making this argument, Alan is essentially alone, and I mean alone,” Bowman said Tuesday, accusing Republicans of seizing on Dershowitz’s argument because it gives them cover not to convict a president in their own party. “What Dershowitz did yesterday was stand up and be a guy with Harvard attached to his name and spout complete nonsense that’s totally unsupported by any scholarship, anywhere.”

Indeed, a statutory crime has never been required for impeachment, dating back to the 14th century, when the British Parliament invented the procedure as a mechanism for dealing with abuses of royal power. The American framers wrote “high crimes and misdemeanors” into the U.S. Constitution, he noted, to include noncriminal abuses of power, and since then, federal judges and a U.S. senator have been impeached for noncriminal conduct.

John Mikhail, a Georgetown University law professor, agreed. He said Dershowitz was able to “cobble together statements here and there in our history, but at the end of the day, it’s really an outlier position in terms of the scholarly consensus — and substantively very weak.”

Mikhail said it was “kind of incoherent” and ignored all of the evidence that has led to the scholarly consensus that an underlying crime is not necessary to convict in an impeachment trial.

House Intelligence Committee Chairman Adam B. Schiff (D-Calif.), the lead impeachment manager, scoffed at the GOP’s new defense: “They fall back on the argument, ‘Okay, he did it. We all know he did it. But we’re going to find a criminal defense lawyer whose expertise is not really constitutional law . . . and make the argument that is effectively, the Constitution says so what? . . . You cannot impeach a president for abuse of power because it’s too nebulous a concept.’ ”

Still, Republicans seized on Dershowitz’s argument that senators need not hear from additional witnesses because even if the reports were true, Trump can’t be removed from office for those actions.

“I actually think what Ken Starr and what Professor Dershowitz [said] is true, which undermines the whole concept of carrying this impeachment forward,” said Sen. Thom Tillis (R-N.C.). “The charges at the extreme don’t rise to the level of impeachment.”

Sen. John Cornyn (R-Tex.) agreed, arguing that Dershowitz “made a good argument that a crime is required.”

“The Constitution says ‘treason, bribery, other high crimes and misdemeanors,’ ” he said. “It talks all about crimes. So impeaching somebody for a non-crime strikes me as novel. I found it pretty compelling.”

Elsewhere around the Capitol, other Republican senators — Mike Crapo (Idaho) and Mike Rounds (S.D.) — expressed similar opinions about Dershowitz’s rationale. That argument “probably gave a lot more peace of mind to people that were wanting to see how to sort through it,” Braun said, noting that he approached Dershowitz after his argument to ask him again: “If Bolton’s revelation in its full form was true, is that impeachable in your opinion . . . and he said no, because it imputes motives.”

Seung Min Kim contributed to this report.