Sen. Mitt Romney Willard (Mitt) Mitt RomneyMomentum growing among Republicans for Supreme Court vote before Election Day Toobin: McConnell engaging in 'greatest act of hypocrisy in American political history' with Ginsburg replacement vote The Memo: Court battle explodes across tense election landscape MORE (R-Utah) said on Monday that he believes it is more likely other Republican senators will support subpoenaing former national security adviser John Bolton John BoltonDiplomacy with China is good for America The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Pence lauds Harris as 'experienced debater'; Trump, Biden diverge over debate prep DOJ launches probe into Bolton book for possible classified information disclosures MORE in the wake of an explosive New York Times report.

Romney said it’s “increasingly apparent” that the Senate should hear from Bolton after the Times reported that he claims in his forthcoming memoir that President Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE tied Ukraine aid to help with investigations into Democrats.

“It’s pretty fair to say John Bolton has relevant testimony,” Romney told reporters. "I think it's increasingly likely that other Republicans will join those of us who think we should hear from John Bolton."

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Bolton’s forthcoming memoir has thrown a curveball into Trump’s impeachment trial, which had appeared to be on track to wrap up this week.

Trump has denied Bolton’s allegation, and GOP allies, including Rep. Mark Meadows Mark Randall MeadowsTrump reacts to Ginsburg's death: 'An amazing woman who led an amazing life' Trump carries on with rally, unaware of Ginsburg's death United Airlines, unions call for six-month extension of government aid MORE (R-N.C.), have argued that it doesn’t change the fact that Ukraine has said it didn’t feel pressure to investigate Democrats including former Vice President Joe Biden Joe BidenMomentum growing among Republicans for Supreme Court vote before Election Day Trump expects to nominate woman to replace Ginsburg next week Video of Lindsey Graham arguing against nominating a Supreme Court justice in an election year goes viral MORE and his son Hunter Biden.

But Democrats have seized on the allegation as evidence that the Senate needs to call new witnesses.

The chamber is expected to vote later this week on whether to call witnesses. If that vote is successful, both sides would then be able to make motions for specific individuals that would be voted on by the Senate.

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Democrats need four Senate Republicans to vote with them to successfully call witnesses.

So far, Romney is the only GOP senator who said he wants to hear from Bolton, though he’s stressed that he’ll make a final decision after opening arguments and questions from senators.

Sens. Susan Collins Susan Margaret CollinsJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally Momentum growing among Republicans for Supreme Court vote before Election Day MORE (R-Maine) and Lisa Murkowski Lisa Ann MurkowskiMomentum growing among Republicans for Supreme Court vote before Election Day Collins: President elected Nov. 3 should fill Supreme Court vacancy Barrett seen as a front-runner for Trump Supreme Court pick MORE (R-Alaska) have both signaled they are open to witnesses but want to make a decision after the initial phase of the trial. They have not weighed in on the Times story.