Sen. Lisa Murkowski Lisa Ann MurkowskiMcConnell locks down key GOP votes in Supreme Court fight Most Americans think winner of election should pick next Supreme Court justice: poll Murkowski: Supreme Court nominee should not be taken up before election MORE (R-Alaska) asked Thursday why 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 should not be called to testify during President Trump Donald John TrumpBiden leads Trump by 36 points nationally among Latinos: poll Trump dismisses climate change role in fires, says Newsom needs to manage forest better Jimmy Kimmel hits Trump for rallies while hosting Emmy Awards MORE's Senate impeachment trial, noting that conflicting accounts about Trump’s decision to delay U.S. aid to Ukraine “weighs in favor” of hearing from additional witnesses.

Murkowski, who is known for her independent streak, is considered a swing vote whether the Senate will call in witnesses like Bolton. Her question Thursday night, during the second day of a question and answer session, could signal where the senator stands.

“This dispute about material facts weighs in favor of calling additional witnesses with direct knowledge. Why should this body not call Ambassador Bolton,” Murkowski asked in a question poised to the White House defense team.

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Murkowski noted in her question that U.S. Ambassador to the E.U. Gordon Sondland Gordon SondlandGOP chairman vows to protect whistleblowers following Vindman retirement over 'bullying' Top Democrat slams Trump's new EU envoy: Not 'a political donor's part-time job' Trump names new EU envoy, filling post left vacant by impeachment witness Sondland MORE and Sen. Ron Johnson Ronald (Ron) Harold JohnsonGOP set to release controversial Biden report Democrats fear Russia interference could spoil bid to retake Senate The Hill's Morning Report - Sponsored by The Air Line Pilots Association - White House moves closer to Pelosi on virus relief bill MORE (R-Wis.), an ally of the president, have said Trump did not withhold $391 million in aid to Ukraine as leverage to press Kyiv to open politically beneficial investigations, including one into a 2020 political rival.

She then said that a New York Times report of Bolton’s unpublished manuscript that says the former Trump official was referring to a direct conversation the president about the aid suggests otherwise.

Patrick Philbin, a member of the president’s defense team, argued that the question is one of precedent: The House voted to impeach Trump before it collected all the evidence it wanted to use in the Senate trial.

“The most important consideration, I think, that this chamber has before it…has to do with the precedent that is established here for what kind of impeachment proceeding this body will accept from now going forward,” Philbin said, warning about setting the “new normal” for future presidential impeachment proceedings.

Philbin argued that the House should’ve pursued Bolton’s testimony, saying that putting the onus of calling in witnesses onto the upper chamber will do grave damage to the Senate as an institution.

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Philbin was echoing a view used by Republicans who do not want to call in new witnesses.

Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellOcasio-Cortez to voters: Tell McConnell 'he is playing with fire' with Ginsburg's seat McConnell locks down key GOP votes in Supreme Court fight Video shows NYC subway station renamed after Ruth Bader Ginsburg MORE (R-Ky.) offered varying reasons why witnesses should not be called, arguing that the House should’ve pursued their testimony during Democrats’ impeachment inquiry rather than placing the responsibility on the Senate and claiming calling witnesses would extend the trial indefinitely.

Democrats, meanwhile, have shot back that the White House went to unprecedented heights to block witnesses — both current and former — from testifying.

And they add that Bolton’s lawyer made clear he would challenge a subpoena for his testimony, which would’ve locked them in a court battle for months — time Democrats say they did not have.

The matter is expected to be voted on on Friday. Democrats will need four Republicans to vote in favor of calling in witnesses – that is, if no Democrats defect from the party-line.