Sen. Susan Collins speaks to reporters after presenting at Fruit Street School on Jan. 10, 2020.

SOUTH PORTLAND, Maine — U.S. Sen. Susan Collins of Maine said Friday she wanted to hear from President Donald Trump’s former national security adviser and the U.S. ambassador to the European Union before voting to acquit Trump of impeachment charges this week.

Maine’s senior senator was one of only two Republicans to join Democrats in a bid to allow witnesses in the Senate’s impeachment trial last week, but it failed and Collins voted with every Republican but Sen. Mitt Romney, R-Utah, to acquit the president of two impeachment charges from House Democrats.

Collins was perhaps the most-watched senator during the process, which she largely declined to comment on while citing her role as a juror. She was one of the last Republicans to announce how she would vote on Tuesday and is facing a targeted challenge from national Democrats in her 2020 bid for a fifth term in a blue-leaning Maine.

On Friday after speaking to a police chiefs’ conference at a South Portland hotel, Collins told reporters she wished she had heard from former White House national security adviser John Bolton and Ambassador Gordon Sondland during the president’s impeachment trial.

An unpublished manuscript from Bolton twice roiled the trial, including when The New York Times reported that the former adviser alleged Trump had told him military aid to Ukraine was on hold because it was tied to the country launching investigations into Democrats.

Trump largely denied those claims, which were tied to Democrats’ two articles of impeaching alleging abuse of power relating to a summer call with the Ukrainian leader and obstructing a congressional probe. Sondland told a House committee there was a “quid pro quo” between the aid and investigations after saying the president told him there wasn’t one.

Collins broke with her party in voting to subpoena Bolton after the Senate had already voted not to call witnesses in the trial, while she said she would have liked to have heard from Sondland because his House testimony was “contradictory.”

“He said that he presumed there was a quid pro quo but nobody ever really challenged him on why he presumed that,” she said.

Collins reiterated on Friday morning that she disapproved of Trump’s conduct but thought it did not meet the constitutional standard of “high crimes and misdemeanors” to remove a president from office and her vote was not a show of support for the president’s actions.

“You don’t try to make predictions, you consider the evidence that is before you,” she said.

While Collins refused to endorse Trump in 2016, she has been forced into difficult votes during his tenure. Her 2018 vote for U.S. Supreme Court Justice Brett Kavanaugh set off a wave of liberal organization against her ahead of her 2020 re-election with more than $10 million spent already on ads focused on the race.

She told CBS News on Tuesday that she believed Trump “learned” from impeachment before walking that back a day later to call the comment “aspirational.” Collins faced fresh criticism from opponents over the initial remark, with House Speaker Sara Gideon, one of four Democrats running for the nomination to face her, saying Trump had “learned nothing.”

Trump was defiant in a celebratory winding speech on Thursday, insisting he “went through hell” and “did nothing wrong.” He has characterized his Ukraine move as “a perfect call,” a characterization senators — including Collins and other Republicans who acquitted him — have rebuked.