Utah 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) said Saturday that it is “very likely” he will be in favor of calling witnesses in the Senate impeachment trial against 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.

However, the GOP lawmaker said he will hold off on making his final decision until after Democratic impeachment managers and the president’s defense lawyers conclude their opening arguments.

"I think it's very likely I'll be in favor of witnesses, but I haven't made a decision finally yet and I won't until the testimony is completed," the Utah Republican said Saturday after the first day of the Trump team’s opening arguments, CNN reported.

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Romney declined to say whether he thought the president’s defense team was effective in the opening hours of their arguments, saying, "I just don't have any comments on the process or the evidence until the trial is over,” CNN reported.

Earlier this month, Romney was the first GOP lawmaker to specifically say that he wanted to hear from former White House 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 course of the impeachment trial.

Romney told reporters at the Capitol that he wants to find out “what he knows” about Trump’s contacts with Ukraine, the central issue in the impeachment effort against the president.

“I would like to be able to hear from John Bolton. What the process is to make that happen, I don’t have an answer for you,” Romney said.

Bolton has yet to be subpoenaed by lawmakers in the trial, and Democrats will need four Republicans to support their efforts if they are going to call the former Trump administration officials or other witnesses.

Bolton has said he would testify if subpoenaed by the Senate.

Fellow GOP 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 (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 (Alaska) have also both indicated an openness to hearing from further witnesses.