Maine Sen. Susan Collins Susan Margaret CollinsThe Hill's Campaign Report: Biden asks if public can trust vaccine from Trump ahead of Election Day | Oklahoma health officials raised red flags before Trump rally Gideon leads Collins by 12 points in Maine Senate race: poll Senate leaders quash talk of rank-and-file COVID-19 deal MORE (R) on Tuesday defended her newly announced decision to vote to acquit President Trump Donald John TrumpBarr criticizes DOJ in speech declaring all agency power 'is invested in the attorney general' Military leaders asked about using heat ray on protesters outside White House: report Powell warns failure to reach COVID-19 deal could 'scar and damage' economy MORE in his Senate impeachment trial, saying he has learned "a pretty big lesson" over his dealings with Ukraine.

Trump's acquittal on Wednesday looks all but certain, with Collins the latest possible swing vote to say she would come down against the two House-passed articles of impeachment.

"I believe that the president has learned from this case," she told Norah O'Donnell of CBS News. "The president has been impeached. That's a pretty big lesson."

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"He was impeached. And there has been criticism by both Republican and Democratic senators of his call," she continued, before predicting: "I believe that he will be much more cautious in the future."

CBS NEWS EXCLUSIVE: Sen. Susan Collins (R-ME) tells @NorahODonnell she will vote to acquit Pres. Trump in the Senate impeachment trial, adding that she believes "the president has learned from this case."



Watch more tonight at 6:30 p.m. ET. https://t.co/oxGYtYgjBw pic.twitter.com/Wv4PmGINZk — CBS Evening News (@CBSEveningNews) February 4, 2020

Collins added in the interview that the president's July conversation with Ukrainian President Volodymyr Zelensky was grounds for reprimand, as she believed Trump should not have mentioned his desire for a criminal investigation into former Vice President Joe Biden Joe BidenThe Memo: Warning signs flash for Trump on debates Senate Republicans signal openness to working with Biden National postal mail handlers union endorses Biden MORE, but added that she did not believe the action fell into the realm of impeachable conduct.

"The president's call was wrong. He should not have mentioned Joe Biden in it, despite his overall concern about corruption in Ukraine," Collins told CBS. "The president of the United States should not be asking a foreign country to investigate a political rival. That is just improper. It was far from a perfect call."

Collins, who is up for reelection in November, was seen as one of the few GOP senators with the potential to side against Trump.

"I'm sure there are going to be people unhappy with me in Maine. All I can do is apply the constitutional standard. And that's my job," she said. "My job is not to weigh the political consequences, but to do impartial justice to live up to the oath that I took."