Critical swing-vote Sen. Lamar Alexander says he will announce Thursday night whether he’s voting to call witnesses in President Trump’s impeachment trial.

The retiring Tennessee Republican’s stance could dictate the outcome of a high-stakes vote on Friday and determine if Trump’s trial ends quickly or is extended weeks with witnesses.

Republicans are optimistic that Alexander will vote against witnesses after he cooperated with two fellow Republicans to submit a question Thursday in the Q&A phase of Trump’s trial.

Alexander joined Sens. Ted Cruz (R-Texas) and Steve Daines (R-Mont.) in asking Democratic impeachment managers to contrast bipartisanship in the Trump case with the Bill Clinton and Richard Nixon impeachments. The Trump case thus far has seen remarkable party cohesion.

Senate Majority Leader Mitch McConnell (R-Ky.) appeared pleasantly surprised when informed that Alexander was submitting the question.

During a brief break for dinner Thursday, Alexander met with fellow swing-vote Sen. Lisa Murkowski (R-Alaska), who also has been open to calling witnesses but non-committal on the vote.

Alexander then walked down a hallway toward a Republican conference dinner where a taco buffet was served. He did not speak with a group of reporters on his way to and from the dinner.

Senate Majority Whip John Thune (R-S.D.) told reporters, however, that he was hopeful that Alexander “will end up in the right place” on the witness vote.

Cruz, who co-submitted the trial question with Alexander, declined to say if he knew his colleague’s stance, and predicted the outcome of the Friday vote on witnesses won’t be clear “until the vote is cast.”

Alexander told a CNN journalist that “I’m going to make my decision after the last question tonight,” likely after 10 p.m., and that he would publicly announce that decision late Thursday.

Two Republicans — Sens. Susan Collins (R-Maine) and Mitt Romney (R-Utah) — have indicated they would like to call witnesses including former National Security Advisor John Bolton, who claims in a forthcoming book that Trump confessed to withholding Ukraine aid to force investigation of Democrats, the central allegation against him.

Collins and Romney only get Democrats to 49 votes, with 51 needed to call witnesses — or perhaps 50, if Chief Justice John Roberts intervenes. Many Republican senators have refused to speak with reporters during the trial, adding to uncertainty.

“I have spoken to Lamar a number of times,” Cruz told reporters during the dinner break Thursday. “In terms of the votes, all 47 Democrats have been clear that they will vote to call additional witnesses. The big question is will four Republicans join the 47 Democrats? Two Republicans, Sen. Romney and Sen. Collins, have indicated publicly that they tend to vote that way and I think there are several other Republicans who may or may not join them.”