Senate Minority Leader Chuck Schumer (D-N.Y.) once again invoked the Watergate scandal in his discussion of Congress' impeachment efforts against President Donald Trump on Friday.

While briefing reporters in the U.S. Capitol on Wednesday, Schumer once again reiterated his call for more witnesses and documentary evidence in the Senate's impeachment trial and criticized Republicans who did not want to do so.

"If my Republican colleagues refuse to even consider witnesses and documents in this trial, this country is headed toward the greatest cover-up since Watergate," Schumer said after once again criticizing President Trump's efforts to get Ukrainian officials to look into suspected corruption last year.

"If my Republican colleagues refuse to even consider witnesses and documents in the trial, what will the president conclude?" Schumer continued. "We all know, he'll conclude he can do it again, and Congress can do nothing about it."

This wasn't the first time this week that Schumer invoked the Watergate scandal — which eventually led to President Richard Nixon's resignation — in an effort to make his case for more evidence in the impeachment trial. On Tuesday, he said that "a steady drip, drip, drip of information" related to the trial was "reminiscent of Watergate."

Schumer's Friday comments were the latest in his efforts to draw out the length of the trial by bringing in more witnesses and documents, a subject that has been a major point of contention between Republicans and Democrats during the trial process. They also come as it appears highly unlikely that there will be enough Republican senators to break ranks and join with Democrats to make Schumer's desire for more witnesses a reality.

Republicans grew optimistic that they have the votes to end the trial this week without having to call more witnesses following a meeting between Senate Majority Leader Mitch McConnell (R-Ky.) and moderate Republican Lisa Murkowski (Alaska) Wednesday. This was later compounded Thursday night after outgoing Republican Sen. Lamar Alexander (Tenn.) announced that he wouldn't be crossing the aisle on the witness issue, contrary to speculation that he might have.

Murkowski announced Friday that she would vote against calling impeachment witnesses.