Alexander is one of a handful of Republican senators who may vote to hear from witnesses during the Senate impeachment trial.
ADVERTISEMENTSen. Lamar Alexander, R-Tenn., a key impeachment swing vote, will on Thursday night reveal whether or not he supports calling witnesses in President Donald Trump's Senate impeachment trial.
Alexander, who's retiring from Congress at the end of the year, is among a small group of Republican senators who had hinted during the trial they could vote to hear from witnesses who had first-hand knowledge of Trump's conduct towards Ukraine.
Former national security adviser John Bolton and acting White House chief of staff Mick Mulvaney are among the witnesses Democrats have called on to testify.
Republican Sens. Susan Collins of Maine, Lisa Murkowski of Alaska and Mitt Romney of Utah were also considered to be top targets for Democrats who want to hear new witness testimony and documentary evidence at the Senate trial. Four Republicans will need to vote alongside all Democrats in order for new witness testimony to be admitted.
Alexander privately huddled with Murkowski during Thursday's dinner break, according to a senior Republican aide close to Alexander. The two lawmakers discussed where they are on witnesses but are not coordinating their final decision, the aide tells NBC News. It's unclear which way he will vote.
Alexander, who served two terms as governor of Tennessee before two unsuccessful runs for president, has a history of bipartisanship. He worked with Senate Minority Leader Chuck Schumer, D-N.Y., and a handful of other Democrats to make it easierfor the Senate to confirm the presidential nominees.
As chair of the Senate Health, Education, Labor and Pensions Committee, The Tennessee Republican worked closely with Sen. Patty Murray, D-Wash., the committee's ranking member, to make sweeping education reforms.
Alexander asked his first question during the Senate trial on Thursday, along with two other senators, in which he pressed the House managers to compare the bipartisanship in the Nixon, Clinton and Trump impeachment proceedings.
"Specifically how bipartisan was the vote in the House of Representatives to authorize and direct the House Committees to begin formal impeachment inquiries for each of the three presidents?" he asked, signaling possible frustration that the House vote against Trump was not bipartisan.
Rep. Zoe Lofgren, D-Calif., who was a House Judiciary Committee staffer during President Nixon's impeachment proceedings and a member of the committee during both the Clinton and Trump impeachments, said neither were truly bipartisan.
"In the Nixon impeachment we look back and we think about the vote on the House Judiciary Committee that ended up bipartisan but it didn't start that way," she said. "When it came to the Clinton impeachment. That was, again, It started out along very partisan lines. And it ended along partisan lines."