WASHINGTON — House Speaker Nancy Pelosi said the House will take steps next week to send articles of impeachment to the Senate, ending Democrats' blockade of President Donald Trump's Senate trial.

In a letter to her Democratic colleagues, Pelosi said Friday she was proud of their ''courage and patriotism" and warned that senators now have a choice as they consider the charges of abuse and obstruction against the president.

"In an impeachment trial, every Senator takes an oath to do 'impartial justice according to the Constitution and laws,'' Pelosi wrote. "Every Senator now faces a choice: to be loyal to the President or the Constitution."

The move could mean the trial starts as soon as next week. Senate Majority Leader Mitch McConnell said Friday afternoon that the Senate is "anxious to get started" and "we'll get about it as soon as we can."

Soon after Pelosi sent out the letter, Trump criticized her in an interview with Laura Ingraham of Fox News. He said that it was "ridiculous" that she withheld the articles.

"She should have sent them a long time ago. It just belittles the process," Trump said. "Nancy Pelosi will go down as the least successful speaker of the House in the history of our nation."

The president also expressed concern about former national security adviser John Bolton's announcement that he would testify in the Senate trial if called. Asked if he would invoke executive privilege to stop it, Trump said, "Well I think you have to for the sake of the office."

Chuck Cooper, an attorney for Bolton, declined to comment.

Pelosi: House moving to send impeachment to Senate next week

House Speaker Nancy Pelosi said the House will take steps next week to send articles of impeachment to the Senate. File/AP

Bolton was present for several of the internal White House discussions about Ukraine policy that were at the heart of the Democrats' impeachment case. The president faces charges of abuse and obstruction over his efforts to urge Ukraine to investigate Democrats.

Since the House vote on Dec. 18 to impeach the president, Pelosi has been in a standoff with McConnell that has consumed Capitol Hill and scrambled the political dynamics. She said she did not want to send the articles to the Senate unless she knew there would be a fair trial with witness testimony.

Pelosi also asked McConnell for details on the structure of the trial so she could decide who to appoint as impeachment managers. McConnell never provided them.

On Friday, Pelosi ended the stalemate by saying she had asked House Judiciary Committee Chairman Jerrold Nadler to be prepared to bring to the floor next week a resolution to appoint managers and transmit the articles of impeachment to the Senate.

"I will be consulting with you at our Tuesday House Democratic Caucus meeting on how we proceed further," Pelosi wrote in the letter to her colleagues. She did not announce a date for the House vote.

The move eases for now the protracted showdown between Pelosi and McConnell over the rare impeachment trial, only the third in the nation's history.

Transmittal of the documents and naming of House impeachment managers are the next steps needed to start the Senate trial. Yet questions remain in the Senate on the scope and duration.

McConnell wants to launch a speedy trial without new witnesses but Democrats point to new evidence that has emerged as they press for fresh testimony, as well as Bolton's willingness to testify.

Despite McConnell's wishes for a speedy trial, some Republicans in his caucus have indicated that they are open to witnesses.

Republican Sen. Susan Collins of Maine, who is up for re-election this year, said in a statement Friday that she is in discussions with some of her GOP colleagues about how they can adhere "as closely as practical" to former President Bill Clinton's trial, which included closed-door witness testimony.

"I am hopeful that we can reach an agreement on how to proceed with the trial that will allow the opportunity for witnesses for both the House managers and the President's counsel if they choose to do so," Collins said. "It is important that both sides be treated fairly."

The House impeached Trump in December on the charge that he abused the power of his office by pressuring Ukraine's new leader to investigate Democrats, using as leverage $400 million in military assistance for the U.S. ally as it counters Russia at its border. Trump insists he did nothing wrong, but his defiance of the House Democrats' investigation led to an additional charge of obstruction of Congress.

As Pelosi has withheld the articles, Republicans have had the leverage, with a slim 53-47 Senate majority, as McConnell rebuffed the Democratic demands for testimony and documents. But Democrats have used the delay to sow public doubt about the fairness of the process as they try to peel off wavering GOP senators for the upcoming votes. It takes just 51 senators to set the rules.

"When we say fair trial, we mean facts, we mean witnesses, we mean documents," said Senate Minority Leader Chuck Schumer, D-N.Y., promising votes ahead. "Every single one of us, in this Senate, will have to have to take a stand. How do my Republican friends want the American people, their constituents, and history to remember them?"

After Pelosi's announcement on Friday, Schumer issued a short statement: ""Senate Democrats are ready for the trial to begin and will do everything we can to see that the truth comes out."

On a July telephone call with Ukraine's new president, Trump asked his counterpart to open an investigation into Democrat Joe Biden, who is running for his party's presidential nomination, and his son Hunter while holding up military aid for Ukraine. A Ukrainian gas company had hired Hunter Biden when his father was vice president and the Obama administration's point man on Ukraine. There is no evidence of wrongdoing by either Biden.

The delay on impeachment has also upended the political calendar, with the weekslong trial now expected to bump into presidential nominating contests, which begin in early February. Several Democratic senators are running for the party's nomination.

It's still unclear who Pelosi will appoint as impeachment managers to prosecute the case in the Senate.

Nadler, D-N.Y., and House Intelligence Committee Chairman Adam Schiff, D-Calif., will most likely lead the team.

What was more certain is that the group will be more diverse than the 1999 team in Clinton's trial, who were all male and white. Pelosi is expected to ensure the managers are diverse in gender and race, and also geographically.

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Associated Press writers Laurie Kellman, Alan Fram, Andrew Taylor, Darlene Superville and Padmananda Rama contributed to this report.