New top story from Time: Trump’s Impeachment Trial Could Be in Its Final Hours After Key Republican Falls in Line to Block Witnesses

President Donald Trump could be headed for a speedy acquittal in his Senate impeachment trial after Republicans secured assurances from a key lawmaker late Thursday night that he would not break with the party to request additional evidence and testimony.

Lamar Alexander, the 79-year-old retiring Tennessee Senator and close ally of Majority Leader Mitch McConnell, announced his decision after the Senators had completed the 16-hour period allotted for written questioning.

“There is no need for more evidence to prove something that has already been proven and that does not meet the U.S. constitutions high bar for an impeachable offense,” Alexander said in a statement. “The constitution,” he continued, “does not give the power to remove the president from office and ban him from this year’s ballot simply for actions that are inappropriate.”

Alexander’s decision comes after a new revelation significantly raised the stakes for hearing from witnesses at the trial earlier this week. According to a leaked manuscript, Trump’s former National Security Advisor John Bolton recounted a conversation in which the President admitted to the core of the charges against him: that he had leveraged military aid to Ukraine to get the country’s government to open probes into Democratic rivals.

Alexander’s decision makes it considerably more likely that Republicans will procure the votes needed to block additional witnesses at the trial.

Earlier on Thursday evening, Maine Sen. Susan Collins announced that she would vote to hear from witnesses from both sides. “I believe hearing from certain witnesses would give each side the opportunity to more fully and fairly make their case, resolve any ambiguities, and provide additional clarity,” she said in a statement.

The focus will now inevitably turn to two of Alexander and Collins’ colleagues: Alaska Sen. Lisa Murkowski and Utah Sen. Mitt Romney. Since Bolton’s account became public on Sunday night, Romney has indicated that he, like Collins, may break with his party, while Murkowski, who left the Capitol Thursday evening saying she would reflect on it, remains a wild card. There is a possible scenario where Chief Justice John Roberts, who is presiding over the trial, could break a tie, although that too remains an open question.

“There’s a lot of uncertainty in terms of what happens with the Presiding Officer,” Indiana Sen. Mike Braun said Thursday, noting that Senators could technically overrule him with 51 votes.

If Republicans do have the necessary votes to block witness testimony, there are still procedural uncertainties over how things will unfold on Friday.

There will be four hours of debate on the issue of witnesses—two for each side–when the trial resumes Friday afternoon as a prelude to the vote. But it is unclear what happens afterwards. Senate Minority Leader Chuck Schumer could force several procedural votes, as he did at the start of the trial. He has kept his plans close to the vest though, only telling reporters on Thursday that “the minority has rights, and we will exercise those rights.”

On Thursday night, Senators seemed in near universal agreement that the following day could stretch into the early hours of the morning. “You’re better off thinking of it as a vote-a-rama, meaning that it could go until 2, 3, 4 in the morning, as opposed to thinking of it as simply two hours on either side,” said South Carolina Sen. Tim Scott.

In the unlikely event that enough Republicans do vote for witnesses, or that Roberts ends up casting a tie-breaking vote for Democrats, there could be a slew of votes on which witnesses to allow.

Democrats have identified three others they want to hear from in addition to Bolton: acting White House Chief of Staff Mick Mulvaney, and White House officials Michael Duffey and Robert Blair.

But both Republicans and the White House have made it clear that, if Democrats get witnesses, they want to call their own. Trump’s attorney Jay Sekulow, for instance, said earlier this week that he wants to hear from Schiff, Hunter Biden, Joe Biden and the whistleblower who drafted the complaint that resulted in the impeachment inquiry.

Despite the many uncertainties still looming, Alexander’s announcement is undoubtedly a boon for both McConnell and Trump, moving them one step closer to completing the trial.

Alexander provided few clues during the first day of written questioning, declining to submit any queries at all. But on Thursday afternoon, hints of his position began to emerge. His first question, submitted with his Republican colleagues Sens. Steve Daines and Ted Cruz, asked the House managers how the partisanship in this presidential impeachment compares with that of Bill Clinton and Richard Nixon.

It was the first suggestion that Alexander, who has a history of working across the aisle, would stay firmly in his party’s line. Later that evening, he joined with one of Trump’s top allies, Sen. Lindsey Graham, along with Murkowski, Cruz and Sens. Dan Sullivan, Rob Portman and Pat Toomey, to ask the White House team why bringing in Bolton would make a difference if they were still arguing the allegations against Trump do not warrant an impeachable offense.

As the White House answered the question, Murkowski scribbled in her notebook, while Alexander looked calmly ahead, listening intently. By the time the House managers were rebutting the response, he had moved to the back of the chamber.

Calls from House managers and Senate Democrats for Bolton’s testimony, already strong, intensified on Thursday, with the lawmakers insisting that a trial without witnesses wasn’t really a trial at all. As House managers responded to written questions from Senators, they repeatedly returned to the narrative of the urgent need to call Bolton.

“No trial, no vindication. No vindication for the President, or anyone else,” Schiff said Thursday afternoon before the start of the trial. “The Constitution requires a fair trial.”

Polls indicated the public was in their corner: a Quinnipiac poll released Jan. 28 showed that 75 percent of voters wanted to hear from witnesses in a trial. But their immediate success always hinged on persuading a small cadre of centrist lawmakers who could cross party lines. And ultimately, Alexander wasn’t one of them.