House Speaker Nancy Pelosi arrives for House Democratic Caucus meeting on Tuesday, Dec. 17, 2019, before a scheduled House Rules Committee hearing on the articles of impeachment against President Donald Trump on Capitol Hill in Washington. Photo: AP Photo/Patrick Semansky.

WASHINGTON - Democrats and Republicans were set to grapple on Tuesday over the rules of engagement for a historic vote set for Wednesday in the U.S. House of Representatives, where President Donald Trump is likely to become the third U.S. president to be impeached.

The Republican president remained in attack mode a day before his expected impeachment in the Democratic-led House, referring to the process in a Twitter post as "this whole Democrat Scam" and calling himself "your all time favorite President."

"Don't worry, I have done nothing wrong. Actually, they have!" Trump wrote.

In what is expected to be a marathon meeting, the House Rules Committee will decide how much time to set aside for debate on Wednesday before lawmakers vote on two articles of impeachment charging Trump with abuse of power and obstruction of Congress over his dealings with Ukraine.

Representative Jerry Nadler - the Democratic chairman of the House Judiciary Committee, which approved the articles of impeachment last week - will miss the Rules Committee meeting because of a family emergency, and Representative Jamie Raskin will represent the Democrats in his place, a congressional aide said. Nadler is expected to be back at the Capitol on Wednesday.

The panel's top Republican, Representative Doug Collins, also will testify before the Rules Committee.

The looming vote promises to bring a raucous, partisan conclusion to a months-long impeachment inquiry against Trump that has bitterly divided the American public as voters prepare for next year's presidential and congressional elections.

The House is expected to approve the impeachment articles largely along partisan lines. The action then moves to the Republican-controlled Senate, where the effort to remove Trump from office faces long odds.

House Democrats accuse Trump of abusing his power by asking Ukraine to investigate former Vice President Joe Biden, a leading Democratic contender to oppose him in the 2020 U.S. presidential election. He is also accused of obstructing Congress' investigation into the matter.

Trump denies wrongdoing and has accused Democrats of conducting a "sham" impeachment to oust him from office.

Lawmakers are expected to offer amendments at the Rules Committee meeting, which could run for 12 hours or more depending on how many of the House's 431 sitting legislators decide to show up and speak.

In the end, the committee will set the rules for the floor debate that will precede the impeachment vote.

FRIENDLIER TERRAIN

The final House vote is expected to fall largely along party lines. Several Democrats from districts that backed Trump in 2016 said on Monday they would vote to impeach him.

"I will vote yes, knowing full well the Senate will likely acquit the President in a display of partisan theater that Republicans and Democrats in Washington perform disturbingly well," Democratic Representative Ben McAdams of Utah said in a statement.

Trump will be on friendlier terrain in the Senate, which is expected to consider the charges in January.

Republicans hold 53 of the Senate's 100 seats, and at least 20 of them would have to vote to convict Trump in order to clear the two-thirds majority required to remove Trump from office. None have indicated they may do so.

Senate Democratic leader Chuck Schumer said he wanted the trial to consider documents and hear testimony from four witnesses, including acting White House Chief of Staff Mick Mulvaney and Trump's former national security adviser John Bolton, saying testimony could sway Republicans in favor of impeachment.

Senate Republican leader Mitch McConnell has suggested the chamber could move quickly to a vote without hearing from witnesses, after House Democrats and the White House make their presentations.

The White House, which has not cooperated in the impeachment inquiry in the House, signaled opposition to Schumer's requests for the Senate trial.

"Why in the world should we be asked to fill in the blanks that the Democrats created? They created these huge holes and canyons in the presentation of their case. It's not up to us to help them fill in the blanks and make their case," presidential adviser Kellyanne Conway told reporters.

Reuters