WASHINGTON -- House Speaker Nancy Pelosi said Friday that she will send articles of impeachment against President Donald Trump to the Senate next week.

"I have asked Judiciary Committee Chairman Jerry Nadler to be prepared to bring to the Floor next week a resolution to appoint managers and transmit articles of impeachment to the Senate," Pelosi wrote to House colleagues.

Impeachment managers are House members who essentially act as prosecutors in a Senate trial of the president. Before the articles can be delivered to the Senate, the managers need to be agreed to by a House vote.

Friday's letter sets up the prospect of a multiweek impeachment trial of Trump to begin in the Senate later this month.

It also poses a dilemma for the five senators seeking the 2020 Democratic presidential nomination. The Iowa caucuses are on Feb. 3, and spending several weeks in Washington, not Iowa, right before the caucus could put their campaigns at a disadvantage.

Pelosi's announcement was made amid mounting pressure on her, not only from Republicans, but increasingly from fellow Democrats to deliver the articles. Once they've been received, the Senate can begin preparations for a trial.

On Thursday, Pelosi told reporters she still needed to see how the Senate would conduct a trial, before she agreed to transfer the articles. "We want to see what they're willing to do, and the manner in which they will do it," she said.

By Friday, her calculus appeared to have shifted, although she did not directly explain why in her letter. "I am very proud of the courage and patriotism exhibited by [House Democrats] as we support and defend the Constitution," she wrote, adding that she would "be consulting" with her caucus next week "on how we proceed further."

Senate Minority Leader Chuck Schumer, D-N.Y., said in a statement later Friday that Democrats in his chamber "are ready for the trial to begin and will do everything we can to see that the truth comes out."

The House voted on Dec. 18 to impeach Trump, but for the past three weeks, Pelosi had refused to send the articles to the Senate. The delay was part of a strategy aimed at forcing concessions out of Senate Majority Leader Mitch McConnell, R-Ky., chief among them, the ability to call witnesses.

McConnell has so far said the question of witnesses should be shelved until partway into the trial itself, as was the case in the 1998 impeachment of former President Bill Clinton. Pelosi rejected that analogy in her letter on Friday.

"The American people have clearly expressed their view that we should have a fair trial with witnesses and documents, with more than 70 percent of the public stating that the President should allow his top aides to testify," she wrote.

"Clearly, Leader McConnell does not want to present witnesses and documents to Senators and the American people so they can make an independent judgment about the President's actions."

Trump was impeached on two articles stemming from his monthslong campaign to pressure Ukraine into launching investigations into Joe Biden and other domestic political opponents. The pressure tactics allegedly included withholding congressionally approved military aid to Ukraine in its war against Russian-backed separatists.

The first article of impeachment charges that Trump abused the power of the presidency, and the second alleges that he obstructed Congress by prohibiting top administration officials from testifying about the Ukraine scheme. Trump has denied any wrongdoing.

Following the articles' passage, Pelosi said she planned to hold them until McConnell assured her he would conduct what Democrats called "a fair process."

Democrats have insisted that any trial of the president include testimony from witnesses, something in which Republicans have so far shown no interest.

But the effort has so far failed to produce results, and the Senate leader said this week he would move forward on Trump's impeachment trial without any Democratic support.

Earlier this week several Senate Democrats and at least one Democratic House committee chair publicly said they thought it was time to send the impeachment articles to the Senate.

Within hours, however, they reversed themselves, with Armed Services Committee Chairman Rep. Adam Smith, D-Wash., insisting he "misspoke," and Sen. Dianne Feinstein, D-Calif., saying "I don't know what happened there ... I did not mean to say that."

It's considered highly unlikely that two-thirds of the GOP-controlled Senate will vote to convict and remove Trump from office. No Senate Republicans have said they support impeaching Trump.

Correction: Five senators are seeking the 2020 Democratic presidential nomination. An earlier version misstated the number.