House Leader Steny Hoyer, D-Md., began by stressing that Trump's action's last week "demand urgent, clear action by the Congress," and praised House Republican Conference Chair Liz Cheney and a handful of Republicans for agreeing with Democrats that Trump ought to be impeached.

"This is the daughter of the former Republican whip and former vice president of the United States of America. She knows of what she speaks, and she said this as well, 'There has never been a greater betrayal by a president of the United States of his office and his oath of Constitution," he said. "This is not, as Liz Cheney said, just some action. She characterized it as the biggest betrayal of any president of the United States in our history."

Hoyer went on to list GOP Rep. John Katko of New York, the ranking Republican on the Homeland Security Committee who Hoyer described as "not some back-bencher on your side of the aisle" and Rep. Adam Kinzinger of Illinois, among the five House Republicans who have publicly stated they'll vote to impeach the president.

"Mr. Kinzinger said this," Hoyer said, "If these actions are not worthy of impeachment, then what is an impeachable offense? There is no doubt in my mind that the president of the United States broke his oath and incited this insurrection."

Hoyer said other Republicans who he has talked to "in the past 24 hours" agree the president's actions are impeachable.

Democrats and Republicans are expected to debate for one hour -- equally divided between Democrats and Republicans -- before a procedural vote ahead of the chamber beginning debate on the impeachment article itself.

Democrat Rep. Jim McGovern, the chairman of the House Rules Committee, setting up that preliminary vote on the terms of the debate, called the Capitol a "crime scene" and the rioters "traitors" and "domestic terrorists" in an assault instigated by Trump, emphasizing, "We wouldn't be here if it weren't for the president of the United States."

McGovern described the day as "a ceremonial role for the Congress -- one that sends a message to the world that democracy persists -- but at a rally a mile and-a-half down Pennsylvania Avenue, Donald Trump was stoking the anger of a violent mob," he began. "He said Vice President Pence has to come through and told the mob to walk down to the Capitol."

"The signal was unmistakable. These thugs should stage a coup so Donald Trump can hang on to power, the people's will be damned. This beacon of democracy became the site of a vicious attack. Rioters chanted, 'Hang Mike Pence,' as a noose and gallows were built. Capitol Police officers were beaten and sprayed with pepper spray. Attackers hunted down lawmakers to hold them hostage or worse," McGovern continued.

"I saw evil, Mr. Speaker. Our country came under attack, not from a foreign nation but from within," he added. He also slammed Republicans for preaching unity from members who voted to overturn a free and fair election.

Republican Rep. Tom Cole -- one of the lawmakers who object to Electoral College results after the violent seige -- called Jan. 6 the "darkest day" of his long career in Washington, but said Democrats, instead of promoting unity, are looking to "divide us further" by pursuing Trump's impeachment.

Cole did not directly defend Trump's actions or rhetoric but argued in Congress, one week before Biden's inauguration, sets up a "flawed process."

The U.S. House of Representatives has gaveled in to consider the second impeachment of President Trump.

Democrats formally introduced an impeachment resolution Monday, charging Trump with "incitement of insurrection" after he told his supporters at a “Save America Rally” to march on the Capitol during Congress’ joint session to count Electoral College votes on Jan. 6.

"He also willfully made statements that, in context, encouraged — and foreseeably resulted in — lawless action at the Capitol, such as: "if you don't fight like hell you're not going to have a country anymore,'" the resolution reads.

“Thus incited by President Trump, members of the crowd he had addressed, in an attempt to, among other objectives, interfere with the Joint Session's solemn constitutional duty to certify the results of the 2020 Presidential election, unlawfully breached and vandalized the Capitol, injured and killed law enforcement personnel, menaced Members of Congress, the Vice President, and Congressional personnel, and engaged in other violent, deadly, destructive and seditious acts," it continues.

"In all this, President Trump gravely endangered the security of the United States and its institutions of Government. He threatened the integrity of the democratic system, interfered with the peaceful transition of power, and imperiled a coequal branch of Government. He thereby betrayed his trust as President, to the manifest injury of the people of the United States," it goes on.

The impeachment article also cited Trump's call with the Georgia Republican secretary of state where he urged him to "find" enough votes for Trump to win the state -- along with the Constitution's 14th Amendment, noting that it "prohibits any person who has 'engaged in insurrection or rebellion against' the United States" from holding office.

As House lawmakers arrived on Capitol Hill Wednesday, they were greeted by the sight of National Guard members dispersed throughout the Capitol complex before debate kicked off -- a stark sight from last week when Capitol Police were found outnumbered.

Expecting the article to pass the House later Wednesday, Speaker Nancy Pelosi is planning to send the article of impeachment over to the Senate next week, according to a source involved in the Democratic leadership deliberations.

This would leave the Senate no choice but to immediately move towards a trial. The exact timing will depend on whether Majority Leader Mitch McConnell decides to call the Senate back in session early -- which he's said he wouldn't do. Under Senate rules, the Senate cannot officially receive any message or bill or resolution from the House unless the Senate is in session, and the chamber is not scheduled to be back until Jan. 19.

But in preparation for that time, Pelosi has named nine members to serve as impeachment managers to argue the case in the Senate to remove Trump from office over his role in last week’s Capitol riot.

Rep. Jamie Raskin, D-Md., a former constitutional law professor who co-authored the article and whose family was present at the Capitol last Wednesday, one day after burying Raskin's son who took his own life, will serve as the lead impeachment manager.

The other managers -- one of rarest assignments for a House member -- are Democratic Reps. Diana DeGette, Colo., David Cicilline, R.I., Joaquin Castro, Texas, Eric Swalwell, Calif., Ted Lieu Calif., Joe Neguse, Colo., Madeleine Dean, Pa., and Del. Stacey Plaskett, Virgin Islands.

"It is their constitutional and patriotic duty to present the case for the President’s impeachment and removal. They will do so guided by their great love of country, determination to protect our democracy and loyalty to our oath to the Constitution," Pelosi said in a statement Tuesday night.

The impeachment managers are a different set from those tapped by Pelosi one year ago for Trump’s first impeachment trial -- then led by Rep. Adam Schiff, D-Calif. During that effort, managers argued the case to remove Trump for pressuring Ukraine’s president to promise to investigate Biden and his son, Hunter.

-ABC News' Jonathan Karl and Chad Murray

The number of National Guard troops deployed around next week's inauguration could rise from at least 10,000 to 15,000, the National Guard’s top general said Monday.

"Support requests from the Secret Service, Capitol Police and Park Police have been authorized to provide up to 15,000 Guard members to meet current and future support requirements," Gen. Daniel Hokanson, the chief of the National Guard Bureau, told reporters on a phone briefing. "They are troops that have been requested to support security, logistics liaison and communication missions."

Hokanson said that there are currently 6,200 Guardsmen in the District, and there would be 10,000 in place by Saturday.

The National Guard has always participated in inaugurations, and there were 9,000 members on hand last year, but because of the coronavirus pandemic, the number had been reduced to 5,000 for 2021. Last week's insurrection at the Capitol changed those plans, and Pentagon spokesperson Jonathan Hoffman additionally made clear that the Guardsmen will be remaining in Washington after Inauguration Day.

"We're not looking at Jan. 20 as the last day and people will pack up and go home at the conclusion of all the events," he said. "There will be some elements that will remain for a brief period to ensure safety and security in the days following the inauguration as well."

Hokanson, the chief of the National Guard Bureau, said no decision has been made yet about whether to arm the Guardsmen but characterized that possibility as an "ongoing discussion."

"Obviously, we're very concerned that we want our individuals to be have the right to self defense," he said.

-ABC News' Luis Martinez