Sen. Susan Collins Susan Margaret CollinsSenate Republicans face tough decision on replacing Ginsburg Democratic senator calls for eliminating filibuster, expanding Supreme Court if GOP fills vacancy What Senate Republicans have said about election-year Supreme Court vacancies MORE (R-Maine) said on Thursday that it's "likely" she would support calling witnesses after the initial phase of the impeachment trial but has not yet made a decision on any particular individual.

"While I need to hear the case argued and the questions answered, I tend to believe having additional information would be helpful. It is likely that I would support a motion to call witnesses at that point in the trial just as I did in 1999," Collins said in a statement, referring to the Clinton impeachment trial.

Collins is viewed as a crucial swing vote in the Senate impeachment trial of President Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE, particularly on the procedural fights over whether additional witnesses should be called or whether documents should be handed over.

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The rules resolution, which has not yet been unveiled, is expected to include a built-in vote after opening arguments and questions from senators on whether additional evidence is needed.

Collins, who is seen as one of the most vulnerable senators ahead of her reelection in 2020, worked to get that language included in the resolution.

Democrats need four Republicans to support their request for witnesses. So far, only Sen. Mitt Romney Willard (Mitt) Mitt RomneySenate Republicans face tough decision on replacing Ginsburg McConnell says Trump nominee to replace Ginsburg will get Senate vote GOP-led panel to hear from former official who said Burisma was not a factor in US policy MORE (R-Utah) has said that he wants to hear from former national security adviser John Bolton John BoltonDiplomacy with China is good for America The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Pence lauds Harris as 'experienced debater'; Trump, Biden diverge over debate prep DOJ launches probe into Bolton book for possible classified information disclosures MORE.

Collins said in her statement that she has not made a decision on calling any particular individual.

"When we reach the appropriate point in the trial, I would like to hear from both sides about which witnesses, if any, they would like to call," Collins said.

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Democrats want to call four individuals: Bolton, acting White House chief of staff Mick Mulvaney Mick MulvaneyMick Mulvaney to start hedge fund Fauci says positive White House task force reports don't always match what he hears on the ground Bottom line MORE, Mulvaney's senior adviser Robert Blair and Michael Duffey, the associate director of national security at the Office of Management and Budget.

They're expected to force votes twice during the trial: first, when the chamber debates the resolution outlining the rules for the trial next week. They can then force votes for a second time after opening arguments and questions from senators.

Collins said she will not support calling witnesses before the initial phase of the trial. Democrats are expected to get no GOP support on the votes they force next week after Republicans lined up behind delaying a decision on witnesses until mid-trial.

"Prior to hearing the statement of the case and the Senators asking questions, I will not support any attempts by either side to subpoena documents or witnesses. Instead, that issue should be addressed at the same point that it was in the 1999 trial," Collins said.

Collins has repeatedly said she wants to follow a process for the Trump impeachment trial that mirrors the Clinton trial.

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She was one of 15 senators currently serving who were also members of the Senate in 1999. She voted to find Clinton "not guilty" on both articles of impeachment and noted in her statement that she supported additional witnesses in 1999.

Collins is one of the most closely watched senators during the upcoming impeachment trial, and faces a near constant train of questions from reporters in the Capitol.

She appeared to knock the media in the opening of her statement, saying "there has been a lot of mischaracterization and misunderstanding about my position on the process the Senate should follow for the impeachment trial."

-- Updated at 6:37 p.m.