House Republican Conference Chair Liz Cheney -- the No. 3 Republican in the House and highest-ranking woman in the Republican Party -- has announced she will vote to impeach Trump for inciting an insurrection at the Capitol.

"Much more will become clear in coming days and weeks, but what we know now is enough," she said in a statement. "The President of the United States summoned this mob, assembled the mob, and lit the flame of this attack. Everything that followed was his doing. None of this would have happened without the President. The President could have immediately and forcefully intervened to stop the violence. He did not."

"There has never been a greater betrayal by a President of the United States of his office and his oath to the Constitution," she said.

Her announcement follows Republican Rep. John Katko of New York becoming the first House Republican to say he will support House Democrats' efforts to remove Trump from office through impeachment.

Republican Rep. John Katko of New York has released a statement saying he will vote to impeach Trump -- becoming the first Republican to publicly voice an expected vote to remove the president from office.

Katko joins at least 218 House Democrats who have signed onto a resolution charging Trump with inciting an insurrection. A House vote could happen as early as Wednesday, one week before Biden's inauguration at the Capitol.

“To allow the president of the United States to incite this attack without consequence is a direct threat to the future of our democracy,” Katko said in the statement. “For that reason, I cannot sit by without taking action. I will vote to impeach this president."

No House Republicans voted to impeach Trump in 2019.

-ABC News' Benjamin Siegel

The first confirmation hearing for one of Biden's Cabinet picks is officially on the Senate schedule for the day before his inauguration -- which is also the earliest day the Senate is likely to accept an impeachment article against Trump from the House.

Department of Homeland Secretary nominee Alejandro Mayorkas' hearing will be at 10 a.m. on Tuesday, Jan. 19, the Senate Homeland Security and Governmental Affairs Committee announced Tuesday.

In the wake of the siege on the Capitol, the incoming Biden administration is making a push to prioritize confirmations for national security nominees, so those officials may assume their roles as early as next week.

Traditionally, the Senate has confirmed national security nominees on Inauguration Day, and did so for Department of Homeland Security secretary nominees in both 2009 and 2017.

Capitol Police have added new security measures to the House of Representatives -- requiring that all members and staff go through metal detectors before they enter the chamber, according to a new memo sent to offices by the acting House Sergeant at Arms.

The memo comes ahead of a vote Tuesday evening on a resolution pressing Vice President Mike Pence to mobilize the Cabinet and invoke the 25th Amendment to remove Trump from office.

Currently, visitors and staff are screened when they enter the Capitol building, but members of Congress are not. There are already metal detectors in place for visitors to the House galleries, which had been shuttered since March because of the pandemic.

Several lawmakers continue to worry about their safety in the wake of last week's Capitol riot -- and Democrats in control of the chamber have expressed concerns about some GOP colleagues and their alleged connections to the organizers. Some Republicans, most notably Rep. Lauren Boebert, R-Colo. have been outspoken about carrying weapons around the Capitol.

"Failure to complete screening or the carrying of prohibited items could result in denial of access to the Chamber," acting Sergeant at Arms Timothy Blodget wrote in the memo.

-ABC News' Benjamin Siegel and Mariam Khan

House Democrats have opened an investigation into what law enforcement and the intelligence community knew about threats to the Capitol ahead of the Jan. 6 siege.

The investigation from the House Intelligence, Oversight, Homeland Security and Judiciary committees will also examine whether anyone with security clearances -- current or former National Security, Defense, Justice or Homeland Security officials -- participated in the riot.

The investigation will also examine the federal law enforcement response in the aftermath of the attack.

"The Committees will conduct robust oversight to understand what warning signs may have been missed, determine whether there were systemic failures, and consider how to best address countering domestic violent extremism, including remedying any gaps in legislation or policy," committee members wrote in a letter to the FBI, DHS and Office of the Director of National Intelligence.

"This still-emerging story is one of astounding bravery by some U.S. Capitol Police and other officers; of staggering treachery by violent criminals; and of apparent and high-level failures -- in particular, with respect to intelligence and security preparedness," the letter later stated.

Democrats plan to request documents and briefings from administration officials as part of the investigation -- just one of several looking into the Capitol attack.

-ABC News' Benjamin Siegel