CNN  — 

Sen. Susan Collins of Maine, a moderate Republican senator up for reelection in 2020, said Tuesday that she would vote to acquit President Donald Trump on both articles of impeachment, dimming the chances that any Senate Republicans will cross party lines to vote to remove the President from office.

Collins was one of two Republicans who voted last week to call witnesses and seek documents in the Senate impeachment trial, in a vote that failed 49-51. But she said she would vote against removing the President over the House’s articles of impeachment when the Senate votes on the final verdict Wednesday.

Collins said that the President’s actions in asking Ukraine to investigate his political rival were “improper and demonstrated very poor judgment.” But she said the House’s case did not meet the burden of removing the President from office.

“I do not believe the House has met its burden that the President’s conduct, however flawed, warrants the extreme step of immediate removal from office,” Collins said. “This decision is not about whether you like or dislike this President or agree with or oppose his policies or approve or disapprove of his conduct in other circumstances. Rather it is about whether the charges meet the very high constitutional standard of treason, bribery or other high crimes or misdemeanors.”

Collins’ decision means that Sen. Mitt Romney of Utah, the other Republican who voted for witnesses, appears to be the only Republican remaining who could cross party lines to convict the President. Romney has yet to say how he is voting.

Wednesday’s final vote on the President’s impeachment trial is a forgone conclusion – the Senate will fall far short of the two-thirds majority required to remove Trump from office – but the vote tally is still unsettled, with several senators remaining publicly undecided.

Since closing arguments ended on Monday, senators have been streaming to the Senate chamber to explain their vote in 10-minute speeches – the first time they’ve been able to speak on the floor since the trial began.

Along with Collins, Sen. Lisa Murkowski of Alaska, another closely watched moderate Republican, announced on the floor this week that she would vote to acquit the President. Murkowski criticized all sides in the explanation of her vote, calling Trump’s conduct “shameful and wrong” but concluding that the House “failed in its responsibilities” by rushing to impeach the President. And she said the Senate “should be ashamed by the rank partisanship that has been on display here.”

Among Democrats, Sens. Joe Manchin of West Virginia, Doug Jones of Alabama and Kyrsten Sinema of Arizona have not said how they will vote on Wednesday.

Manchin spoke on the floor on Monday, but said he has not yet made up his mind on whether to vote to remove Trump from office. Manchin proposed a resolution to censure the President instead, but he acknowledged that it was unlikely to have any traction.

“That’s a shame,” he said, adding that he would still “see what the mood is after Wednesday.”

Jones and Sinema have yet to speak on the floor, which is open for senators until Wednesday’s vote at 4 p.m. Jones said Tuesday that he has “tentatively” made a decision and would announce it Wednesday morning.

Sen. Joni Ernst, a Republican up for reelection in Iowa, said Tuesday that she would vote to acquit Trump, adding that she’s angry and thinks most people are upset by the impeachment process.

“This is a very dark path to go down,” she said.

Sen. Gary Peters, a Michigan Democrat running for reelection in a state Trump won in 2016, said he would vote to hold the President accountable for his actions. “It is clear that the President betrayed the trust of the American public placed in him to fully execute his constitutional responsibilities,” Peters said. “This betrayal is by definition a high crime and misdemeanor. If it does not rise to the level of impeachment and removal, I am not sure what would.”

This story has been updated with additional developments Thursday.

CNN’s Ted Barrett, Ali Zaslav and Clare Foran contributed to this report.