Representative Ken Buck, a conservative Colorado Republican who played a central role in ousting Kevin McCarthy from the speakership, said he will not seek re-election next year, citing his party’s election denialism and many members’ refusal to condemn the Jan. 6. 2021, assault on the Capitol.
Mr. Buck, serving his fifth term from a sprawling district east of Denver after a career as a prosecutor, said he had decided to step aside because his differences with the contemporary Republican Party had grown too great to continue serving in its ranks. He condemned his party’s reluctance to take on big issues and said it had badly damaged itself with voters.
“We lost our way,” said Mr. Buck, 64, who announced his intentions in interviews and a video news release. “We have an identity crisis in the Republican Party. If we can’t address the election denier issue and we continue down that path, we won’t have credibility with the American people that we are going to solve problems.”
His announcement followed one earlier Wednesday by Representative Kay Granger, Republican of Texas and chair of the Appropriations Committee, who said she also would not run again next year. She too played a prominent role in the speaker showdown. Others are likely to follow suit given the chaos that has engulfed the Republican-led House.
Mr. Buck’s decision comes after several months in which his frustration and dissatisfaction with his party have been evident. He is the third House member to declare this week that he will not seek re-election next year after Representative Earl Blumenauer, Democrat of Oregon and a House member since 1996, said Monday he would not run again.
In the thick of the speaker fight, Representative Debbie Lesko, Republican of Arizona, announced that she would leave Congress after her current term, declaring that, “Right now, Washington is broken.”
Ms. Granger, 80, surprised her colleagues by refusing to back Representative Jim Jordan of Ohio, the party’s nominee for speaker, on the floor. That prompted some calls for her to lose her gavel on the Appropriations Committee. She voted instead for Representative Steve Scalise of Louisiana, the No. 2 Republican who had won the first internal G.O.P. contest for the nomination to succeed Mr. McCarthy but withdrew when he determined he did not have the votes on the floor. She is bumping up against party term limits for her time as chair, and is part of an all-female team leading the House and Senate spending panels for the first time in Congress’s history.
“Although I am not running for re-election, I plan to serve out the remainder of my term and work with our new speaker and my colleagues to advance our conservative agenda and finish the job I was elected to do,” she said in a statement.
Mr. Buck, one of eight Republicans who voted with Democrats to oust Mr. McCarthy, is also the second G.O.P. member of Congress to break publicly with his party in announcing he would not run again, and to denounce the cultural dominance of the hard right and its continuing allegiance to former President Donald J. Trump. Senator Mitt Romney, Republican of Utah, announced in September that he would not seek a second term, saying the “Trump wing of the party talks about resentments of various kinds and getting even and settling scores and revisiting the 2020 election.”
Mr. Buck, a former federal and state prosecutor, was dogged by some verbal gaffes and lost a 2010 Senate race to Senator Michael Bennet, a Democrat. He briefly considered running for the Senate again in 2014 but instead won the House seat in the more conservative, rural eastern portion of Colorado and has remained since.
A fiscal hawk who blames both parties for refusing to address Social Security and Medicare as drivers of the federal deficit, Mr. Buck said repeatedly that Mr. McCarthy did not follow through on his promises to focus on cutting spending and institute new oversight of federal agencies and their budgets.
In addition to opposing Mr. McCarthy, Mr. Buck also rejected Mr. Jordan for the speakership, saying that Mr. Jordan’s refusal to accept the 2020 election results and his support of activities on Jan. 6 were disqualifying.
“We promise to solve problems, but we can’t acknowledge what happened on Jan. 6,” said Mr. Buck. “These Jan. 6 defendants are not political prisoners. They hit police officers. They broke windows.” Mr. Buck keeps a poster saying “Back the Blue” outside his office and considers himself a strong supporter of law enforcement.
He ultimately did back Representative Mike Johnson of Louisiana for speaker despite Mr. Johnson’s own effort to reverse the election results through a legal challenge that ultimately failed, but he said that Mr. Johnson had followed the proper legal route through the courts.
Mr. Buck has also questioned the grounds for Republican pursuit of impeachment charges against President Biden and has faced a backlash for his multiple breaks with the party, including death threats. He would likely face a primary challenge if he did run but said he was confident he could prevail.
He also faulted Republicans on foreign policy and said the party has strayed far from the ideological underpinnings of Ronald Reagan, with many of his Republican colleagues failing to recognize the need to support Ukraine in its war with Russia.
“If America is not strong, the world’s in chaos,” he said. “It’s not just in our interest to be there. The world depends on a big brother out there making sure people don’t fight.”
Mr. Buck said he intended to finish his term but would begin exploring other opportunities. He has substantially raised his media profile as a Republican willing to challenge current party orthodoxy and said he thought there were better ways to participate outside the House.
“I have a passion for staying in this fight,” he said. “Whether it’s a tech issue or foreign policy issue or other issues, I think that our traditional conservative values have a place in this marketplace of ideas and need to be promoted.”
