Watch live: Senate to hold key vote on impeachment witnesses

Jan. 31 (UPI) -- President Donald Trump could be acquitted Friday in his Senate impeachment trial, now that adding witnesses and new evidence to the proceeding appears unlikely.

Republican leaders believe they have enough support to defeat Democratic proposals to include a few administration witnesses and new evidence. The Senate closed the questioning stage of the trial on Thursday and will next consider all motions.

This is the stage at which Democrats hoped to persuade at least four GOP senators to join them and vote to include key witnesses like former national security adviser John Bolton and and White House chief of staff Mick Mulvaney.

The chamber will vote on the motions later Friday after what's expected to be a several-hour floor fight. The vote will follow a round of closing arguments from both sides, beginning at 1 p.m. EST Friday.

The biggest blow to Democrats' hopes came late Thursday when Sen. Lamar Alexander of Tennessee, who's considered one of only four likely "swing" voters, told reporters he will oppose including witnesses. It's expected that Democrats must have the support of Alexander and Sens. Susan Collins of Maine, Lisa Murkowski of Alaska and Mitt Romney of Utah to approve the motion to add witnesses.

"There is no need for more evidence to prove something that has already been proven and that does not meet the United States Constitution's high bar for an impeachable offense," Alexander said.

"It was inappropriate for the president to ask a foreign leader to investigate his political opponent and to withhold United States aid to encourage that investigation. When elected officials inappropriately interfere with such investigations, it undermines the principle of equal justice under the law. But the Constitution does not give the Senate the power to remove the president from office and ban him from this year's ballot simply for actions that are inappropriate."

Collins said Thursday she will vote for witnesses, and Romney has also indicated he will support the measure. Murkowski hasn't yet said which way she will vote.

Should the bid to call witnesses fail, Republicans are then expected to raise a motion to acquit Trump on both articles of impeachment -- abuse of power and obstruction of Congress, related to his dealings with Ukraine last year and the House inquiry that followed.

At that point, Democrats can try to prolong the trial by offering amendments intended to force Republican senators into difficult political votes. That could push Friday's session into early Saturday. Sen. Rand Paul, R-Ky., predicted Democrats could extend the session to 12 hours.

"We'll take a crucial vote on whether we will debate having witnesses and documents in this trial," Senate Democratic leader Charles Schumer said Thursday night. "Four Senate Republicans -- just four -- can ensure that we get the truth. A trial without witness and documents would render any acquittal of President Trump meaningless."

Other possible scenarios Friday include a 50-50 split on the witness vote, in which case Supreme Court Chief Justice John Roberts could cast the deciding vote. If he declined to vote, the motion would fail by default.

If Democrats win the vote to include witnesses, their testimony could extend the trial for a couple of weeks.

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