Senate Republicans are optimistic they’ll vote to conclude President Trump’s impeachment trial as soon as Friday and defeat a motion to call new witnesses to testify.

As of Wednesday, only three Republican senators were publicly considering a vote to call witnesses, and one of them, Sen. Lisa Murkowski of Alaska, huddled in the morning with Majority Leader Mitch McConnell in his Capitol office.

Two other GOP lawmakers said to be weighing a vote to call witnesses signaled they would vote against the move.

Sen. Pat Toomey, a Pennsylvania Republican, said he was “very, very skeptical,” he would see a need to vote for additional witnesses.

Sen. Cory Gardner, a Colorado Republican up for reelection in a battleground state, announced Wednesday he wouldn’t vote to call witnesses.

The vote margin is believed to be razor thin.

Republican Sens. Susan Collins of Maine and Mitt Romney of Utah appear likely to call for additional witnesses, while Murkowski’s vote is still up in the air.

Sen. Lamar Alexander, a Tennessee Republican who is not running for reelection, has not indicated whether he will vote for calling witnesses and said he would decide at the end of the trial.

Republicans control 53 votes.

If Collins, Romney, and Murkowski all vote for additional witnesses, it would result in a 50-50 tie, assuming all Democrats vote for witnesses.

A tie vote would defeat the motion to call additional witnesses. But Democrats may move to ask Chief Justice John Roberts to intervene to break the tie, which appears to have occurred on minor votes during the 1868 impeachment trial of President Andrew Johnson.

Republicans blocked a Democratic motion at the start of the trial that would have authorized Roberts to subpoena witnesses and documents.

While it’s not clear whether Roberts would even cast a tie-breaking vote, Republican leaders hope to avoid any uncertainty by limiting their defections to two lawmakers.

If the Senate defeats a motion to call witnesses, it will move to end the trial with votes on the two impeachment articles.

Republicans met privately for lunch before the impeachment trial on Wednesday.

Lawmakers did not discuss witnesses, they told reporters as they left the lunch and headed into the Senate trial.

“I’m optimistic,” Sen. John Cornyn, a Texas Republican and the former Senate majority whip, said. “People have legitimate questions. Part of the difficulty is that no one has done any of this before.”

There are just 15 sitting senators who served during the Clinton impeachment trial, among them Collins.

Collins reminded reporters on Wednesday that she supported hearing witness testimony during the Clinton trial, although the witnesses had already been grilled during an investigation by independent counsel Ken Starr.

Democrats are seeking witnesses House lawmakers did not interview, including former national security adviser John Bolton, who claims in an unpublished book that Trump wanted to block Ukraine security aid until the country investigated Democrats, including former Vice President Joe Biden.

“I’ve said from the beginning that I felt it was likely we would lean toward witnesses, treating each side fairly, in order to clarify and answer some questions,” Collins said. “That remains my position.”

Romney told reporters Wednesday he wanted to hear from Bolton and would agree to a Republican witness as well.

McConnell is steering his Republican conference away from a vote to call additional witnesses, arguing it would extend the trial by weeks or longer but lead to the same outcome — an acquittal of the president.

“Right now, some more members are still assessing what they heard and determining what they need to get to a final conclusion,” said Senate Majority Whip John Thune of South Dakota.

Many Republicans told the Washington Examiner they did not support additional witnesses, in part because they believe it was the responsibility of the House impeachment managers, led by House Intelligence Committee Chairman Adam Schiff of California, to gather all evidence before sending the two impeachment articles to the Senate.

The House heard testimony from 17 witnesses over several weeks in both closed-door interviews and public hearings. It impeached the president on Dec.18 on a party-line vote, without any support from the GOP.

“Why would we prolong a bad process that keeps the Senate from working?” said Sen. Kevin Cramer, a North Dakota Republican. “We are not Adam Schiff’s fishing hole. If he wants to bring articles of impeachment later and build a better case, that’s up to him.”

Republicans are warning the undecided senators in their caucus that a vote to call witnesses would not lead to a narrow list.

While Democrats called 17 witnesses, Republicans have never called a witness in the case.

“If we allow one more witness, then we should let the president have a number of them, until such time that the president is satisfied,” Cramer said. “That would lead to a long, protracted process that comes to the same conclusion.”