Friday will be a make-or-break moment in 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 as Republicans try to bring the proceedings to a close.

Senators will hold a crucial vote on whether to call new witnesses or compel documents as part of the Senate’s proceeding.

Though Trump is all but guaranteed to be acquitted at the end of the trial, Friday’s vote is a turning point that will determine what comes next, including how long it will last.

ADVERTISEMENT

The Senate is expected to convene by 1 p.m. on Friday. Senators are warning that if Republicans successfully block witnesses, senators are likely to move quickly to Trump’s acquittal on Friday night or early Saturday.

Before a vote on witnesses, both Trump’s legal team and House managers get up to two hours each to make their cases to the Senate, according to a resolution passed last week on the rules for the trial.

What happens after that? There are a few scenarios to watch for.

Scenario One: The Senate rejects calling witnesses and moves to acquit Trump

This appears to be the most likely outcome, as the pool of potential Republican votes is quickly shrinking.

ADVERTISEMENT

Democratic senators are reviewing their procedural options for forcing GOP senators to take a round of politically tough votes. Even after it became clear that Republicans had the votes to pass the rules resolution last week, Democrats forced an hours-long fight over amendments.

“We’re looking at all of our parliamentary options to try to force as many votes as we can to put Republicans on the record,” said Sen. Chris Murphy Christopher (Chris) Scott MurphyDemocratic senator calls for 'more flexible' medical supply chain to counter pandemics The Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon GOP chairman to release interim report on Biden probe 'in about a week' MORE (D-Conn.).

Murphy also appeared frustrated by talk among Republicans about wrapping the trial on Friday.

“What’s the point of any of this?” he said, questioning if GOP senators had already decided to skip witnesses and closed-door deliberations.

How long Democrats will be able to slow-walk the end of the trial is unclear. Sen. Rand Paul Randal (Rand) Howard PaulSecond GOP senator to quarantine after exposure to coronavirus GOP senator to quarantine after coronavirus exposure The Hill's Morning Report - Sponsored by National Industries for the Blind - Trump seeks to flip 'Rage' narrative; Dems block COVID-19 bill MORE (R-Ky.) predicted that the Senate would be voting for 12 hours on Friday, indicating that senators are preparing for a long day.

Senate Minority 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 (D-N.Y.) declined to tip his hand but noted that “the minority has rights, and we will exercise those rights.”

ADVERTISEMENT

But Republicans say they are prepared to grind it out and stay in session until Trump is acquitted.

A GOP aide joked that McConnell would face a “revolt” if the leader agreed to delay the final votes, underscoring how eager some Republicans are to get the trial, and the around-the-clock work schedule, behind them.

“As we did with the organizing resolution, we’ll be prepared to stay through here completion,” Barrasso said.

Scenario Two: The Senate deadlocks in a 50-50 tie

One option that has sparked days of speculation around the Capitol is that the Senate’s vote could result in a 50-50 tie on the issue of calling witnesses.

Normally when the Senate deadlocks, Vice President Pence is taxied to the chamber so he can cast a deciding vote. But Pence does not have a role in the Senate’s trial, as Supreme Court Chief Justice John Roberts is the presiding officer.

If Roberts casts a tie-breaking vote, he would put himself in the middle of a fierce political fight.

With Collins to vote to allow witnesses, Democrats would need to win over two more GOP "yes" votes to force the deadlock.

Scenario Three: The Senate votes to call witnesses

House Intelligence Committee Chairman Adam Schiff Adam Bennett SchiffTop Democrats call for DOJ watchdog to probe Barr over possible 2020 election influence Overnight Defense: Top admiral says 'no condition' where US should conduct nuclear test 'at this time' | Intelligence chief says Congress will get some in-person election security briefings Overnight Defense: House to vote on military justice bill spurred by Vanessa Guillén death | Biden courts veterans after Trump's military controversies MORE (D-Calif.) pitched senators Thursday on the idea that if they agreed to call witnesses, depositions could be limited to one week.

“Can we take one week to hear from these witnesses?” Schiff asked. “I think we can. I think we should. I think we must.”