Former Vice President Joe Biden opposed additional witnesses during the Senate impeachment trial of President Bill Clinton, a fact that comes as Democrats try to get former National Security Adviser John Bolton to tesify in the ongoing impeachment trial of President Trump.

Politico obtained a memo on Thursday written by then-Delaware Sen. Biden in January 1999 that was sent to the Democratic caucus in the middle of the Clinton impeachment battle.

“The Senate may dismiss articles of impeachment without holding a full trial or taking new evidence. Put another way, the Constitution does not impose on the Senate the duty to hold a trial,” Biden said to his Democratic colleagues. “In a number of previous impeachment trials, the Senate has reached the judgment that its constitutional role as a sole trier of impeachments does not require it to take new evidence or hear live witness testimony.”

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The leaked transcript of Bolton's upcoming book had renewed efforts by Democrats to introduce new witnesses in the Senate trial in addition to the 17 witnesses that testified in the House before the articles of impeachment were adopted. However, Republicans also called on Biden as well as his son, Hunter Biden, to become witnesses in order to testify about his son's ties to the Ukrainian company Burisma during his tenure as vice president.

President Trump declared "game over" on Wednesday after a clip from August 2019 had surfaced showing Bolton claiming that combating "corruption" in Ukraine was a "high priority" for the Trump administration.

Bolton also called Trump's communications with Ukrainian President Volodymyr Zelensky "warm and cordial," without mentioning any misconduct. It seemingly contradicted reported assertions in Bolton's forthcoming book that Trump explicitly told him he wanted to tie military aid to Ukraine to an investigation into Joe and Hunter Biden.

Another clip surfaced of leading House impeachment manager Adam Schiff, D-Calif, expressing that Bolton had a "lack of credibility" during a 2005 interview when Bolton was up for a nomination as ambassador to the United Nations under then-President George W. Bush.

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"And particularly given the history, where we've had the politicizing of intelligence over WMD [weapons of mass destruction], why we would pick someone who the very same issue has been raised repeatedly, and that is John Bolton's politicization of the intelligence he got on Cuba and other issues, why we would want someone with that lack of credibility, I can't understand," Schiff had said.

All eyes have been on a handful of senators, who are being swayed by colleagues on both sides to either call for witnesses or wrap up the impeachment trial. It is expected that a final vote for additional witnesses will take place Friday evening.

Fox News' Gregg Re contributed to this report.