The Senate impeachment trial is increasingly expected to drag out until next week -- and potentially through President Trump's planned State of the Union address on Tuesday night -- despite the widespread expectation of acquittal in the end.

Sources familiar with negotiations tell Fox News the trial cannot end on Friday and will continue into next week -- possibly Wednesday -- as senators must contend with motions and potential debate by senators on the floor or in closed session.

Senate Majority Leader Mitch McConnell and Democratic Leader Chuck Schumer have not yet hammered out a proposal on how to move forward, Schumer said Friday afternoon, but signaled Democrats may try to force a debate and put senators in a position where they'd have to defend their votes.

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"We are going to use whatever power we have... to prevent it from being rushed through, but right now there is no agreement," Schumer said during a break in the trial.

The timing is especially fluid since the resolution senators passed to open the impeachment trial does not prescribe how to end it. That means the length of motions and timing for procedures are being developed on the fly.

One portion of the trial did come into focus Friday: Republicans have the votes to shut down any new witnesses from testifying in the trial after Sens. Lamar Alexander, R-Tenn., and Lisa Murkowski, R-Alaska, announced they won’t defect.

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While they won't get the witnesses, Democrats want to ensure senators take the time to debate the issue anyway -- and in public.

“Mitch McConnell wants this over as fast as possible with as little attention as possible,” Sen. Sherrod Brown, D-Ohio, said Friday. “That’s why today I’m going to fight to ensure the American people can hear our deliberations.”

Brown has teamed up with Sens. Richard Blumenthal, D-Conn., and Dick Durbin, D-Ill., on two motions to prevent closed-door deliberations and force senators to explain their votes in public.

Unlike typical Senate votes, the rules for impeachment require that any debate among senators take place in secret. Each senator can speak for 10 minutes apiece on a vote on witnesses and 15 minutes each on the final question of whether or not to acquit the president.

Democratic senators will put forth two motions that will force a debate on the two big looming votes -- witnesses and the articles of impeachment -- which would automatically extend the time of the trial. They propose that the debate be out in the open, rather than in a closed session.

The motions would need the support of 51 senators to pass.

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Blumenthal rejected any criticism that Democrats are trying to extend the trial until past the Iowa caucuses, which would keep four 2020 White House hopefuls away from the campaign trail and past Trump’s planned State of the Union address on Tuesday.

He said the timing of these events “are totally irrelevant."

"Pardon me for seeming somewhat cavalier about it, but we're talking about an impeachment trial. Nothing we do as senators will be more important," Blumenthal said.

Democrats making the case for more witnesses in the trial were dumbfounded that Republicans wouldn’t sign on, especially as new information kept leaking out in real-time.

Shortly before the trial resumed on Friday, The New York Times broke another story on ex-national security adviser John Bolton’s manuscript. In it, Bolton claims Trump directed him to help with his pressure campaign to get damaging information on Democrats from Ukraine.

Trump gave the orders during a May Oval Office meeting that included White House chief of staff Mick Mulvaney, the president’s personal lawyer Rudy Giuliani and White House counsel Pat Cipollone, who is spearheading Trump’s defense in the impeachment trial, the report said.

“How absolutely outrageous that The New York Times should be doing the investigative work that the Senate is too cowardly to do?” Blumenthal said. “You know we should be thankful we have a free press that is uncovering the truth... They are doing the job that the United States Senate should be doing, but it has abdicated its responsibility.”

Trump has denied Bolton’s claims and dismissed him as a disgruntled ex-employee trying to sell a book.

“I never instructed John Bolton to set up a meeting for Rudy Giuliani, one of the greatest corruption fighters in America and by far the greatest mayor in the history of N.Y.C., to meet with President [Volodymyr] Zelensky. That meeting never happened,” Trump said in a statement.

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Several GOP senators grumbled at the prospect of the trial continuing past Friday. Many expressed frustration that Trump got impeached on what they believe is a flimsy case and they want the trial to end as soon as possible.

“Let’s go and get this over with for the sake of the American people,” Sen. Lindsey Graham, R-S.C., said.

Sen. Mike Braun, R-Ind., said Trump will be able to give a State of the Union address on Tuesday successfully even if he hasn’t been acquitted just yet.

“He would be able to do almost anything most other individuals couldn't,” Braun said.

Fox News' Chad Pergram and Jason Donner contributed to this report.