Collins, who is up for reelection in November, said she was voting to acquit because the House failed to "met its burden of showing that the president's conduct, however flawed, warrants the extreme step of immediate removal from office."

Collins is part of a small group of Republican senators who have criticized Trump ahead of Wednesday's votes on the articles of impeachment. With 67 votes needed to convict, Trump is all but guaranteed to be acquitted.

Murkowski announced Monday night that she would vote to acquit but called Trump's behavior "shameful and wrong."

"His personal interests do not take precedence over those of this great nation. ... Degrading the office, by actions or even name calling, weakens it for future presidents, and weakens our country," she said.