"As we have said from the start, the actions of that day were lawless and as wrong as wrong can be. Our Capitol should never be compromised and those who broke the law deserve to face legal repercussions and full accountability," McCarthy announced in the letter.
"Unfortunately, one year later, the majority party seems no closer to answering the central question of how the Capitol was left so unprepared and what must be done to ensure it never happens again," he continued. "Instead, they are using it as a partisan political weapon to further divide our country."
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McCarthy went on that Rep. Rodney Davis (R-Ill.), ranking member of the House Administration Committee, would be sending out a memo on measures congressional offices can make to guard the Capitol against future threats, "steps that the current majority party is negligent in acting upon."
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His denouncement of the Jan. 6 investigation comes after he pulled all of his GOP candidates from the House Select Committee probing Jan. 6 to protest House Speaker Nancy Pelosi's (D-Calif.) choice to deny two of his picks.
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"Unless Speaker Pelosi reverses course and seats all five Republican nominees, Republicans will not be party to their sham process and will instead pursue our own investigation of the facts," McCarthy announced in a statement back then.
Pelosi appointed Republican Reps. Adam Kinzinger (Ill.) and Liz Cheney (Wyo.) to sit on the committee, and Cheney was named Vice-Chair. More than 40 conservative figures asked McCarthy last month to dismiss Kinzinger and Cheney from the House GOP conference "due to their egregious actions" as part of the panel.
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Before the Committee's first hearing in July, McCarthy doubted its ability to reach fair conclusions in its investigation.
FROM CONTROVERSY TO COMPASSION: DANIEL SNYDER'S JAW-DROPPING GIFT LEAVES NATION IN AWE
"You've got a Committee chair that questioned the election of George Bush. You've got a committee chair of this who was suing the President. You've got a Committee chair of this who believes Republican senators are equal to terrorists they should be on the terrorist watch list," the minority leader announced back then.
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"Two questions for this entire Committee should be: why were we so ill-prepared for that day and how can we make sure this never happens again, and that's what should drive the Committee," he went on.
Pelosi pushed back on Republican criticism at the time. "We have a beautiful Committee, a Select Committee that is bipartisan, patriotic, solemn, and serious," Pelosi announced, according to CNN.