Alaska Republican Sen. Lisa Murkowski, considered one of the possible swing votes in the Trump impeachment trial, announced on the Senate floor Monday night that she "cannot vote to convict" President Trump.

Murkowski, whose comments closed out a day of debate on the floor over the articles of impeachment, said the "Constitution provides for impeachment but does not demand it in all instances." While most Republican senators are expected to vote to acquit Trump, Murkowski had been considered a possible vote against the president.

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In her floor speech, she said Trump's "behavior was shameful and wrong" with Ukraine but argued against removing him from office, calling for voters to make a judgment in November's election.

"The response to the president's behavior is not to disenfranchise nearly 63 million Americans and remove him from the ballot," she said. "The House could have pursued censure and not immediately jumped to the remedy of last resort."

The Alaska senator added: "The voters will pronounce a verdict in nine months and we must trust their judgment."

Murkowski made news last week as she opposed calling witnesses in the trial, amid speculation she could side with Democrats to prolong the trial. She told reporters at the time that she was "frustrated and disappointed and angry at all sides."

A separate swing-vote senator, Democrat Joe Manchin of West Virginia, suggested earlier Monday he may not vote to impeach Trump, although he said he had not fully made up his mind. He also used part of his speech on the Senate floor to call for the legislative body to censure Trump instead.

Murkowski's comments wrapped up a busy day on the Senate floor that saw the House impeachment managers and the president's defense team give closing arguments before senators began their debate on the articles of impeachment.

Democrat Rep. Adam Schiff implored those few Republican senators who have acknowledged Trump's wrongdoing in the Ukraine matter to prevent a “runaway presidency” and stand up to say “enough.”

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“For a man like Donald J. Trump, they gave you a remedy and meant for you to use it. They gave you an oath, and they meant for you to observe it,” Schiff said. "We have proven Donald Trump guilty. Now do impartial justice and convict him.”

"History will not be kind to Donald Trump," Schiff said, adding that those lawmakers who vote to acquit the president will be tied to Trump “with a cord of steel."

The president's defense countered the Democrats have been out to impeach Trump since the start of his presidency, nothing short of an effort to undo the 2016 election and to try to shape the next one, as early primary voting begins Monday in Iowa.

“Leave it to the voters to choose,” said White House counsel Pat Cipollone.

He called for an end to the partisan “era of impeachment.”

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Trump was impeached in December on two charges: that he abused his power like no other president in history when he pushed Ukraine to investigate rival Democrats, and he then obstructed Congress by instructing aides to defy House subpoenas.

But key Republicans have decided the president's actions toward Ukraine do not rise to the level of impeachable offense that warrants the dramatic political upheaval of conviction and removal from office.

The debate on the Senate flor will continue tomorrow with his acquittal in Wednesday's vote is all but assured.

Fox News' Chad Pergram and The Associated Press contributed to this report.