Senate Democratic Leader Charles Schumer Chuck SchumerRepublican senator says plans to confirm justice before election 'completely consistent with the precedent' Video of Lindsey Graham arguing against nominating a Supreme Court justice in an election year goes viral Graham signals support for confirming a Supreme Court nominee this year MORE (N.Y.) on Friday ratcheted up pressure on Supreme Court Chief Justice John Roberts to break a possible tie vote on a motion to consider subpoenas of additional witnesses and documents, which could extend 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 impeachment trial for weeks.

Schumer to this point has focused on putting pressure on four moderate Senate Republicans to break ranks and vote for 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, among others. But with Sen. Lamar Alexander Andrew (Lamar) Lamar AlexanderMcConnell locks down key GOP votes in Supreme Court fight Alexander backs vote on Trump Supreme Court nominee: What Democrats 'would do if the shoe were on the other foot' Toobin: McConnell engaging in 'greatest act of hypocrisy in American political history' with Ginsburg replacement vote MORE’s (R-Tenn.) announcement Thursday that he will vote against subpoenas, Roberts is now Democrats’ best hope.

“If it’s a tie, it will be up to the chief justice. The chief justice knows every trial has witnesses and documents,” Schumer told reporters Friday morning, though he declined to discuss the scenario at length.

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The prospect of a 50-50 tie on the crucial procedural question depends on the last undecided Republican, 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 (Alaska), who said she would make an announcement Friday morning on how she would vote.

If she joins Sens. Susan Collins Susan Margaret CollinsMcConnell 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-Maine) and Mitt Romney Willard (Mitt) Mitt RomneyGOP set to release controversial Biden report McConnell locks down key GOP votes in Supreme Court fight Will Republicans' rank hypocrisy hinder their rush to replace Ginsburg? MORE (R-Utah) in voting for subpoenas, then the motion to consider new evidence would be deadlocked 50-50.

Senate Republican leaders have argued for weeks that the motion to call new witnesses and documents should fail on a 50-50 vote, but there’s precedent for a chief justice breaking a tie on a procedural question in an impeachment trial.

Then Chief Justice Salmon P. Chase broke two ties on motions to adjourn in President Andrew Johnson’s 1868 impeachment trial. And a motion in the trial to prevent the chief justice from breaking a tie was defeated.

Even so, Democrats view the prospect of Roberts settling the argument over whether new evidence should be weighed as a long shot because it would risk politicizing the court.

“The chief justice breaking a tie is a very last resort to uphold the credibility and trust of our justice system. If necessary, the chief justice might decide to break the tie. I think there’s a powerful argument for it. I think the odds are he will decide against” doing that, said Sen. Richard Blumenthal (D-Conn.).