Sen. 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) said on Monday that a bombshell New York Times report on 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's upcoming book bolsters the case for witnesses and has prompted behind-the-scenes talks among senators.

"The reports about John Bolton's book strengthen the case for witnesses and have prompted a number of conversations among my colleagues," Collins said in a statement.

Collins, who is up for reelection in 2020 and viewed as a key swing vote, reiterated that she is "likely" to support calling witnesses as part of the impeachment trial. But she added that she believes the decision should wait until after opening arguments from both sides and senators get the chance to ask questions.

ADVERTISEMENT

The Times reported on Sunday night that Bolton 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, including former Vice President Biden and his son Hunter Biden.

The report has injected a new dose of chaos into the Senate's debate over witnesses only days before the chamber is expected to vote on whether or not to allow additional witnesses and documents. Collins was part of a small group of senators who worked to the language guaranteeing the vote into the rules resolution.

Democrats will need four Republicans to vote with them to open the door to calling witnesses. After the initial up-or-down vote, both sides are expected to be able to make motions for specific witnesses and the Senate would vote on those requests.

Collins's statement came shortly after 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) told reporters that he thought it was "increasingly likely" that additional GOP senators will support calling Bolton.

“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."

Sen. 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) has also signaled she is open to witnesses but is waiting to make a decision until after the initial phase of the trial. She has not weighed in on the Times report.

Every GOP senator, including Collins, voted against an effort to subpoena Bolton as part of the rules resolution that passed last week.