WASHINGTON — House Democrats leading the investigation into the Jan. 6 attack on the Capitol by a pro-Trump mob named Representative Liz Cheney of Wyoming on Thursday as the committee’s vice chairwoman, elevating the role of a Republican who has been a vocal critic of former President Donald J. Trump’s lies about the 2020 election.
The announcement effectively makes Ms. Cheney the special committee’s second-ranking member, an unusual move for the majority party in the House, which typically grants that position to one of its own. But her appointment to the panel has been part of a break with convention from the start, given that Democrats nominated her and another Republican, Representative Adam Kinzinger of Illinois, in a bid to bring bipartisan credibility to an investigation that most other G.O.P. lawmakers had denounced and worked to thwart.
“Representative Cheney has demonstrated again and again her commitment to getting answers about Jan. 6, ensuring accountability, and doing whatever it takes to protect democracy for the American people,” Representative Bennie Thompson, Democrat of Mississippi and the committee chairman, said in a statement announcing the move. “Her leadership and insights have shaped the early work of the select committee and this appointment underscores the bipartisan nature of this effort.”
It comes as the special committee is ramping up its investigation into the violence that engulfed the Capitol as supporters of Mr. Trump stormed the building in his name, brutalizing police officers and delaying for hours the official counting of electoral votes to formalize President Biden’s victory.
The committee sent record preservation demands this week to 35 technology firms naming hundreds of people whose records they might want to review, including 11 of Mr. Trump’s most ardent allies in Congress, according to several people familiar with the documents who were not authorized to speak about its contents.
Representative Kevin McCarthy of California, the House Republican leader, has threatened to retaliate against any company that complies with the request.
Mr. McCarthy led the charge to strip Ms. Cheney of her Republican leadership post over her continued denunciation of Mr. Trump’s attempts to overturn the results of the 2020 election. This week, Representative Andy Biggs, Republican of Arizona and leader of the ultraconservative Freedom Caucus, circulated a letter calling on Mr. McCarthy to expel both Ms. Cheney, a staunch conservative whose father served as vice president, and Mr. Kinzinger from the Republican conference.
House Republicans voted on May 12 to oust Representative Liz Cheney of Wyoming from their leadership ranks for her refusal to stay quiet about President Donald J. Trump’s election lies.
- Backlash to Impeachment Vote: In January, Ms. Cheney issued a stinging statement announcing that she would vote to impeach Mr. Trump. In the statement, which drove a fissure through her party, she said that there had “never been a greater betrayal by a president of the United States” than Mr. Trump’s incitement of a mob that attacked the Capitol on Jan. 6. She was among 10 Republicans who voted to impeach him. A group of Mr. Trump’s most strident allies in the House called on her to resign from her leadership post.
- Leadership Challenge: In February, Ms. Cheney fended off a challenge to strip her of her leadership position in a secret ballot vote. Even as a majority of House Republicans opposed impeaching Mr. Trump, most were not prepared to punish one of their top leaders for doing so — at least not under a blanket of anonymity.
- Censure: Ms. Cheney also faced opposition from the Wyoming Republican Party, which censured her and demanded she resign. Ms. Cheney rejected those calls and urged Republicans to be “the party of truth.”
- New Challenge: Ms. Cheney continued her blunt condemnation of Mr. Trump and her party’s role in spreading the false election claims that inspired the Jan. 6 attack, prompting a new push to oust her from her leadership role. This time, the effort was backed by Representative Kevin McCarthy, the minority leader.
- Removal: Ms. Cheney framed her expulsion as a turning point for her party and declared in an extraordinary speech that she would not sit by quietly as Republicans abandoned the rule of law. She embraced her downfall and offered herself as a cautionary tale in what she is portraying as a battle for the soul of the Republican Party. The removal came by voice vote during a brief but raucous closed-door meeting in an auditorium on Capitol Hill.
- Impact and Analysis: What began as a battle over the party’s future after the violent end to the Trump presidency has collapsed into a one-sided pile-on by Team Trump against critics like Ms. Cheney, a scion of a storied Republican family. The episode, a remarkable takedown that reflected the party’s intolerance for dissent and unswerving fealty to the former president, has called attention to internal party divisions between more mainstream and conservative factions about how to win back the House in 2022.
- Successor: On May 14, House Republicans elected Representative Elise Stefanik of New York, a vocal defender of Mr. Trump, as their No. 3 leader. Ms. Stefanik pledged to maintain a focus “on unity” as conference chair, but she has also drawn criticism from some hard-right Republicans who have questioned her conservative bona fides.
“Congresswoman Cheney and Congressman Kinzinger are two spies for the Democrats that we currently invite to the meetings, despite our inability to trust them,” Mr. Biggs wrote in the letter, a copy of which was obtained by The New York Times.
Mr. Biggs, who promoted false claims of widespread election rigging in the run-up to the Jan. 6 attack, is among the Republicans whose social media and phone records the select committee is seeking to preserve. In his letter, he proposed changing rules for the Republican caucus to expel any member who accepts a committee assignment from Democrats, a step that Mr. McCarthy has suggested in the past would be appropriate.
“We cannot trust these members to sit in our Republican conference meetings while we plan our defense against the Democrats,” Mr. Biggs wrote.
Ms. Cheney said in a statement that she was pleased to accept the post as the committee’s No. 2.
“Every member of this committee is dedicated to conducting a nonpartisan, professional, and thorough investigation of all the relevant facts regarding Jan. 6 and the threat to our Constitution we faced that day,” Ms. Cheney said. “I have accepted the position of vice chair of the committee to assure that we achieve that goal. We owe it to the American people to investigate everything that led up to, and transpired on, Jan. 6th. We will not be deterred by threats or attempted obstruction and we will not rest until our task is complete.”