Democrats, meanwhile, are holding out hope that Alexander will be their hero in the mold of the late Sen. John McCain, whose extraordinary vote derailed the GOP’s effort to repeal Obamacare. Though Alexander would never blindside McConnell the way McCain did, he is widely believed to be a Republican who could be receptive to Democrats’ message that the Senate needs to hear more evidence.

“There is an opportunity here for Sen. Alexander, who has long been a leader in crafting bipartisan resolutions to impasses, to play a significant, even a historic role,” said Sen. Chris Coons (D-Del.), who has spoken with Alexander about witness testimony. “He is so well-respected in his caucus that there are a number of other senators that are also looking to him.”

Alexander is unlikely to be the 51st vote for witnesses and throw momentary control of the Senate to the Democrats. More likely, if he’s feeling the need to hear new evidence in the trial, other Republicans would join him and scramble plans on how to handle witnesses and documents.

Yet at the moment, GOP leaders are not worried about Alexander, according to a Republican senator and aides privy to party strategy. They believe Alexander is likely to side with McConnell and help wrap up the trial.

But publicly, Republicans are giving him plenty of leeway and refusing to predict where he will end up. And if he is signaling how he will vote, it’s likely directly to McConnell and to no one else.

“All senators make their own decisions on how to vote,” said Sen. John Barrasso (R-Wyo.), the No. 3 Senate Republican.

Moreover, Republicans believe that Democrats’ string of late-night votes ahead of the trial’s opening arguments — which Republicans had said they would not support — alienated Alexander and other on-the-fence GOP senators.

“I thought [Tuesday] night as the night went on, it became easier and easier for him to be one of us. They were making it so easy to vote against their amendments,” said Sen. Kevin Cramer (R-N.D.), a Trump ally. “After [that], he might not be as committed to it.”

Alexander declined to comment for this story. He’s been coy in recent interviews and said “maybe” he will vote for witnesses or “maybe not.” He’s also been quiet in party strategy meetings, according to attendees, and has said publicly he will make his decision after senators’ 16-hour question-and-answer period that will start early next week.

Each Republican has a different set of factors influencing them on witnesses, and most see no reason to anger Trump or McConnell and open up a chaotic new stretch of the impeachment trial.

For Collins, Murkowski and Romney, seeking witnesses could help burnish their independent bona fides.

Alexander’s calculus might be most interesting. He’s retiring at the end of the year, so he is somewhat immune to political retribution. But he’s also close friends with McConnell and is eager to pass a bill lowering health care costs before he leaves office, which Trump would need to sign into law. Any move Alexander makes will likely be negotiated directly with McConnell, for whom he has often served as a back-channel to Democrats, including Minority Leader Chuck Schumer (D-N.Y.).

Alexander also once worked for former Sen. Howard Baker (R-Tenn.), who played a crucial role in challenging President Richard Nixon during Watergate.

“I would hope he has Howard Baker in his mind,” said Sen. Dick Durbin (D-Ill.), “who stepped up and showed his courage time and again when it came to excessive partisanship.”

Alexander has sided with Democrats occasionally, most notably on immigration reform in 2013, but also against Trump’s national emergency declaration. He keeps his cards close: Even when it was clear Alexander would oppose the president’s move to unilaterally seize funds for a border wall, he refused to divulge how he would vote until the last minute.

In the interim, Republicans are making clear that bucking Trump and McConnell would freeze up the Senate for weeks and crater other priorities.

Former Attorney General Michael Mukasey gave a presentation to Senate Republicans on Wednesday about how cumbersome it would be to subpoena someone like former national security adviser John Bolton. Mukasey told the senators that it could take weeks or months to work out how to question Bolton and overcome the barriers of executive privilege, according to an attendee.

That made GOP leaders feel even better about defeating the witness vote next week. And Democrats are feeling worse.

“I was much more optimistic last week than I am this week about winning the vote on witnesses. Because I think that pressure [from McConnell] is happening,” said Sen. Chris Murphy (D-Conn.). “I thought by this week there would be a critical mass of Republicans.”

Still, many senators are wondering what exactly is on Alexander’s mind.

“I know Lamar fairly well,” said Sen. Mike Braun (R-Ind.). “I don’t know where he’ll be.”