WASHINGTON (Reuters) - The Democratic-led U.S. House of Representatives will send formal impeachment charges against President Donald Trump to the Senate as early as next week, House Speaker Nancy Pelosi said on Friday, setting the stage for his long-awaited trial.

Here is what could happen over the coming weeks:

Week of January 13

Pelosi said on Friday that she had asked U.S. House Judiciary Committee Chairman Jerrold Nadler to be prepared to introduce a resolution next week to formally transmit the charges against Trump to the Senate. The resolution would also appoint a group of House members as “managers” tasked with prosecuting the case against Trump before the Senate.

The House could vote on the resolution as soon as Tuesday.

Pelosi’s announcement ended a standoff with U.S. Senate Majority Leader Mitch McConnell, who rejected her proposal.

The Democratic-controlled House voted on Dec. 18 to impeach Trump, but for weeks Pelosi held off on formally transmitting the impeachment package to the Senate in an effort to pressure Republicans who control the chamber to conduct a full-scale trial that includes witness testimony from top Trump aides.

U.S. President Donald Trump speaks during an event to announce proposed rollbacks to the National Environmental Policy Act regulations in the Roosevelt Room of the White House in Washington, U.S., January 9, 2020. REUTERS/Kevin Lamarque

Mid-January to late January

The exact timing of the trial will depend on when the House moves the impeachment papers to the Senate.

U.S. Chief Justice John Roberts would preside over the trial. House managers would present their case against Trump, and the president’s legal team would respond. Senators would act as jurors.

McConnell has said that, once the charges are formally submitted to the Senate, he will back a resolution that would set initial rules for the trial but postpone a decision on whether to hear from witnesses.

The Kentucky Republican has not yet published a draft of the resolution but he said it would be “very similar” to one adopted in January 1999 during the impeachment of former President Bill Clinton.

That resolution set deadlines for the prosecution and defense to submit “trial briefs” that laid out their cases in writing. The resolution also allocated 24 hours for representatives of each side to make oral arguments and set aside 16 hours for senators to ask them questions.

The Clinton resolution referenced by McConnell did not resolve whether witnesses would be called. A follow-up resolution allowing for three witnesses to testify in videotaped depositions passed later along a party-line vote.

Late January to early February

It is still possible congressional Democrats will succeed in their push to hear from witnesses during the trial. If McConnell’s resolution on initial trial rules is adopted, as expected, senators would likely vote after the trial has started on whether to introduce witness testimony sought by the Democrats.

The Senate now has 53 Republicans, 45 Democrats and two independents who usually vote with the Democrats. That means four Republicans would need to cross party lines and join Democrats in requesting witness testimony.

Trump’s former national security adviser John Bolton has said he would testify before the Senate if issued a subpoena, a surprise development that could potentially strengthen the case that Trump should be removed from office.

Democrats hope to hear from Bolton and three current White House officials, including acting chief of staff Mick Mulvaney. Republicans could conceivably try to call witnesses of their own.

Trump is unlikely to be removed from office, however, because under the U.S. Constitution that would require the support of two-thirds of the Senate.