Washington (CNN) Sen. Susan Collins of Maine on Thursday night became the first Republican senator to break rank and announce support for witnesses and documents in the impeachment trial of President Donald Trump.

"I worked with colleagues to ensure the schedule for the trial included a guaranteed up-or-down vote on whether or not to call witnesses. I believe hearing from certain witnesses would give each side the opportunity to more fully and fairly make their case, resolve any ambiguities, and provide additional clarity," Collins, who had previously signaled support for calling witnesses, said in a statement.

"Therefore, I will vote in support of the motion to allow witnesses and documents to be subpoenaed."

Collins' announcement, however, was quickly overshadowed minutes later by news that Republican Sen. Lamar Alexander of Tennessee would oppose calling witnesses, a decision that all but ensures the trial will come to a swift end without hearing from witnesses or subpoenaing documents.

Ahead of Friday's crucial witness vote , Democrats had hoped four Republican would break ranks to give them the 51 votes needed to move ahead with further votes to determine who to subpoena. And while an explosive New York Times report detailing an unpublished draft manuscript by former national security adviser John Bolton added brief uncertainty to the GOP's vote count, Alexander's decision Thursday night appears to have evaporated all options for a fourth Republican to join the Democrats in Friday's vote.

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