House Speaker Nancy Pelosi said Thursday she will “soon″ transmit the articles of impeachment against President Donald Trump.

Pelosi’s remarks came as pressure began mounting from within her own party to forge ahead with Trump’s impeachment trial.

″I’m not holding them indefinitely,” Pelosi told reporters at the Capitol, according to the Associated Press. “I’ll send them over when I’m ready. That will probably be soon.”

Despite Democrats' professed sense of urgency in passing House impeachment articles against the president last month, Pelosi has delayed sending the charges over, or name the trial's House managers, until Senate Majority Leader Mitch McConnell announces how the trial will proceed.

Senate Minority Leader Chuck Schumer (D-N.Y.) and other House Democrats have been demanding additional witnesses be called during a Trump trial, thus stalling any scheduling of a trial.

President Bill Clinton was impeached on perjury and obstruction of Congress charges on Dec. 19, 1998. He was acquitted by the Senate on Feb. 12, 1999. Fourteen senators from that trial still remain in office. Here's how they voted. Susan Collins, R-Maine. Not guilty on both counts Michael D. Crapo, R-Idaho. Guilty on both counts Richard Durbin, D-Illinois. Not guilty on both counts Mike Enzi, R-Wyoming. Guilty on both counts Dianne Feinstein, D-California. Not guilty on both counts Charles Grassley, R-Iow

On Wednesday, Democratic senators joined Republicans in calling on Pelosi to send over the articles. U.S. Sen. Chris Murphy (D-Connecticut) told CNN, "My hope is that we'll be able to get the trial started next week.

"I think if we're trying to create leverage on the Republicans, that leverage really exists when we put them on the record on motions to call witnesses," he said.

Another Connecticut Democrat, U.S. Sen. Richard Blumenthal, told the network he’d like to “begin the trial tomorrow. As a former prosecutor, I'm ready to go to court."

»MORE: How today's U.S. senators voted on Bill Clinton's impeachment

Even U.S. Sen. Dianne Feinstein (D-California) is anxious to get underway, telling Politico, "the longer it goes on the less urgent it becomes. So if it's serious and urgent, send them over. If it isn't, don't send it over."

Donald Trump has become the third American president to be impeached. Trump has been charged with abuse of power and obstruction of Congress. Led by Democrats, the U.S. House of Representatives passed the articles of impeachment on Dec. 18, 2019. Trump will face trial in the GOP-controlled Senate in 2020, a presidential election year. Presidents Andrew Johnson and Bill Clinton were also impeached. Neither was removed from office.

McConnell already has enough votes to defeat any Democratic notions of calling witnesses who did not testify during Trump's House impeachment hearings. Two GOP moderates, Susan Collins of Maine and Lisa Murkowski of Alaska, both agree with McConnell that a Trump impeachment trial should follow the guidelines of Bill Clinton's 1999 trial.

»MORE: McConnell has enough votes to block witnesses during impeachment trial

U.S. Sen. Lindsay Graham (R-S.C.) told Fox News Pelosi's impeachment dam "is about to crack." Graham said he plans to introduce a resolution Thursday calling on House Democrats to send the articles over.

Impeachment was established in the U.S. Constitution as a way to accuse a president of a crime and then hold a trial to determine if guilty. The first step requires a U.S. House member to introduce an impeachment resolution. The House speaker directs the judiciary committee to hold a hearing to decide whether to put the full measure to a vote by the full chamber. A majority of the committee must approve the resolution. If approved, it moves to a full vote on the House floor. If a majority of the House vot

"You said it was urgent," Graham said. "If you believe it to be urgent, send it to the Senate for disposition."

»MORE: Pelosi demanding McConnell release Senate's impeachment trial plans

Trump is only the third sitting president in American history to be impeached, joining Andrew Johnson and Clinton. On Thursday, he took to social media again to deny any wrongdoing:

The two articles of impeachment by House Democrats — abuse of power and obstruction of Congress — point to Trump pressuring Ukraine to investigate 2020 political rival Joe Biden while withholding as leverage military aid the country relies to counter Russia as well as his efforts to block the House investigation.

»MORE: Who are the major players in a Trump impeachment trial?

The Constitution requires a two-thirds majority in the Senate to convict in an impeachment trial, thus making Trump’s actual removal from office highly unlikely in the GOP-controlled Senate.