House Speaker Nancy Pelosi (D-Calif.) said Thursday that President Donald Trump "will not be acquitted" by the Senate in his impeachment trial unless the chamber goes along with Democrats' demands to call more witnesses.

During her weekly press briefing in the U.S. Capitol, Pelosi made the case that, even if the Senate does vote to acquit President Trump of the charges leveled by the House, it won't be a real acquittal unless the Senate does what Democrats have asked for and call for more witness testimony in the trial.

Asked whether she thought Trump would be "chastened" by Congress' impeachment efforts or "emboldened because the Senate will have acquitted him," the speaker quickly responded that Trump "will not be acquitted."

The rationale of this prediction wasn't based on the potential final vote count, but on the perceived legitimacy of the trial if no more witnesses are called.

"You cannot be acquitted if you don't have a trial," Pelosi explained. "And you don't have a trial if you don't have witnesses and documentation."

Pelosi's statement comes against a backdrop of questions about whether Republican senators might break ranks to join their Democratic colleagues' calls to call witnesses and/or subpoena evidence.

Meanwhile, Republicans have grown 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.

The question of more witnesses — particularly former national security adviser John Bolton — has been the subject of intense discussion on Capitol Hill this week following reports of allegations about the president's withholding of Ukraine military aid contained in the manuscript of Bolton's forthcoming book, as well as a Wednesday statement by House Foreign Affairs Committee Chairman Rep. Eliot Engel (D-N.Y.) about a phone call the two had in September.

If Bolton does end up being called as a witness, Republicans have warned about the possibility calling former Vice President Joe Biden, Hunter Biden, and others to testify about the Ukrainian corruption concerns underlying the impeachment efforts in return.

"If people want witnesses, we're going to get a lot of witnesses," Sen. Lindsey Graham (R-S.C.) warned Tuesday in reference to the possibility of a witness trade-off between Democrats and Republicans. "I'll make a prediction: There will be 51 Republican votes to call Hunter Biden, Joe Biden, the whistleblower and the DNC staffer [Alexandra Chalupa] at a very minimum."