Minutes later, the seven impeachment managers — who will prosecute Trump at the trial — led the formal march to the Senate with the newly signed articles in tow. The House sergeant-at-arms and House clerk led the procession.

The procession involved a slow, silent walk through Statutory Hall, through the Capitol Rotunda and eventually to the Senate. The rare and arcane tradition speaks to the uniqueness of moment, with Trump now the third president in history to be impeached.

Although Chief Justice John Roberts is expected in the Capitol Thursday to swear in senators, the trial won't get underway until next week after Congress returns following the Martin Luther King Jr. holiday.

“We are here today to cross a very important threshold in American history,” Pelosi said in floor remarks just before the vote. Rep. Collin Peterson (D-Minn.) was the lone Democratic "no" vote.

In her floor speech, the speaker noted how she resisted for months moving forward with impeachment despite building pressure within her caucus, declaring Trump "wasn't worth it."

Speaker Nancy Pelosi leads an engrossment ceremony to sign article of impeachment on Wednesday that begins the Senate trial of President Donald Trump. (M. Scott Mahaskey/Politico) | M. Scott Mahaskey/Politico

But once the Ukraine scandal surfaced, in which Trump allegedly tried to aid his reelection campaign by pressuring the country's president to investigate Joe Biden, Pelosi said she could no longer resist moving ahead.

“He crossed a threshold. He gave us no choice," Pelosi said of Trump.

Senate Majority Leader Mitch McConnell (R-Ky.) began laying the groundwork for the trial on Wednesday afternoon, then set the schedule for Thursday.

At noon the House impeachment managers will exhibit their articles of impeachment. At 2 p.m. Roberts arrives to be sworn in by Senate Pro Tempore Chuck Grassley (R-Iowa) to preside over the trial. Roberts will then swear in all 100 senators as jurors.

After that the Senate will likely head home for the weekend and "the trial will commence in earnest on Tuesday," McConnell said.

“This is a difficult time for our country. But this is precisely the kind of time for which the framers created the Senate," he said. "I am confident this body can rise above short-termism and factional fever and serve the long-term best interests of our nation.”

The House voted to impeach Trump on Dec. 18, charging him with abuse of power and obstruction of Congress for using his office and government resources to pressure Ukraine and then stonewalling the House's efforts to investigate the scandal.

The GOP-controlled Senate is expected to acquit Trump, but as Pelosi has repeatedly noted, his presidency will forever be accompanied with the asterisk of impeachment. Trump is only the third president in history to be impeached.

“And yes it is a fact – when someone is impeached, they are always impeached. It is true, once someone is impeached it cannot be erased," Pelosi said Wednesday.

The impeachment debate in the House and Senate has been marked by sharp partisanship, even more so than the impeachment of President Bill Clinton.

In one sign of the bitterness that's lasted throughout the process, the two spokesmen for McConnell and Pelosi sparred on Twitter just before the procession over whether the articles would technically be received by the Senate on Wednesday or Thursday.

Earlier in the day, Pelosi appointed a team of seven House Democrats to serve as prosecutors, led by her close ally House Intelligence Chairman Adam Schiff (D-Calif.).

In addition to Schiff, Pelosi named House Judiciary Chairman Jerry Nadler (D-N.Y.), Zoe Lofgren (D-Calif.), Hakeem Jeffries (D-N.Y.), Jason Crow (D-Colo.), Val Demings (D-Fla.) and Sylvia Garcia (D-Texas) as managers.

"What is at stake here is the Constitution of the United States. This is what an impeachment is about,” Pelosi said, flanked by her new managers, whose names had remained strictly secret even to other members of Democratic leadership until less than an hour before the announcement.

Under the rules of the Senate, Trump is summoned and given a time to respond. And during the trial, senators are expected to be in the chamber for all proceedings and are largely prohibited from talking, even having to write down questions they would like to ask.

Pelosi made clear she hand-picked the Democrats who will present the strongest possible case against Trump — both substantively and procedurally — to the Senate.

“The emphasis is on litigators. The emphasis is on comfort level in the courtroom,” Pelosi said, explaining the team she assembled. “The emphasis is on making the strongest case to protect our Constitution.”

The group met for the first time on Wednesday for an initial planning meeting in the House basement.

Schiff, a former prosecutor turned House Intelligence Committee chairman, has earned the trust from across the caucus as he argued the public case against Trump for his role in the Ukraine scandal in a slate of public hearings this fall.

Every one of the impeachment managers has a background in practicing law or law enforcement. All but one — Crow — served on the committees leading the investigations into Trump, hearing dozens of hours of closed-door depositions that ultimately resulted in the president’s impeachment in December.

The group could hardly look more different from the 13 white men who prosecuted former President Bill Clinton in 1999. Pelosi’s team includes three women and four men, as well as two members of the Congressional Black Caucus and a member of the Congressional Hispanic Caucus.

Pelosi made a concerted effort to tap Democrats who don’t come from the traditional liberal power centers: Crow is from Colorado. Garcia is from Texas and Demings is from Florida. Still, more than half of the group hails from New York or California.

Pelosi and her prosecution team used the Wednesday press conference to make a final plea to the Senate to bring in new witnesses and unearth new documents that hadn’t been available to the House trial.