"These allegations demand that the Senate put political biases aside, and make good faith efforts to listen to arguments from both sides and thoroughly review facts and evidence," Romney said.

Romney's statement comes as the Senate's impeachment trial is expected to get underway in earnest on Tuesday when the chamber debates and passes a resolution outlining the rules for the trial.

Both House managers and Trump's legal team would have 24 hours each, spread out over two days, to make their initial arguments, according to the text of the resolution circulated on Monday night.

After that senators would have 16 hours to ask questions in writing through the chief justice. The rules also guarantee a vote mid-trial on "whether it shall be in order to consider and debate under the impeachment rules any motion to subpoena witnesses or documents."

Romney, in statement, indicated that he would support the resolution arguing that "overall, it aligns closely with the rules package" approved during the 1999 trial of then-President Clinton.

"If attempts are made to vote on witnesses prior to opening arguments, I would oppose those efforts," Romney said.

While a majority of Republican senators have indicated that they will vote to acquit Trump at the end of the Senate proceeding, Romney, who has had high-profile clashes with the president, has also kept a tight lid on his thinking heading into the trial.

Romney added on Monday that he viewed the impeachment effort as "difficult," "divisive" and something that "further inflames partisan entrenchment."

"There is inevitable political pressure from all sides. I have spent — and will continue to spend — many hours in careful deliberation about what this process and its potential outcomes could mean for our country. The best we in the Senate can do is strive to meet the obligations outlined by our founding fathers," he said.