The party is "ignoring self-evident truths" for "self-serving lies," he said.
Colorado Rep. Ken Buck on Wednesday announced he won't be seeking reelection and, in a sharply worded statement explaining his decision, he blamed the election denialism that has been embraced by some fellow conservatives in the House.
"Too many Republican leaders are lying to America," Buck said in a video released on social media, "claiming that the 2020 election was stolen, describing Jan. 6 as an unguided tour of the Capitol and asserting that the ensuing prosecutions are a weaponization of our justice system."
"These insidious narratives breed widespread cynicism and erode Americans' confidence in the rule of law," Buck said.
He continued: "It is impossible for the Republican Party to confront our problems and offer a course correction for the future while being obsessively fixated on retribution and vengeance for contrived injustices of the past."
Even before his announcement, Buck had broken with some of his colleagues over Jan. 6 and the 2020 election -- a position that, polling shows, also put him at odds with how many Republican voters have said they feel -- and became a notable dissenter in the party's recent speakership fight, which consumed the House for several weeks.
Buck helped block Judiciary Chairman Jim Jordan, R-Ohio, from winning the speakership in the leadership scramble after Kevin McCarthy was deposed from the top spot.
Buck was also one of the eight Republicans who, along with the Democratic minority, voted to "vacate" McCarthy's speakership in early October.
He has said he took issue with how the budget process was handled under McCarthy.
Of Jordan, he told ABC News last month, "Jim at some point, if he's going to lead this conference during the presidential election cycle ... is going to have to be strong and say Donald Trump didn't win the election."
In his statement on Wednesday, however, Buck spoke more broadly.
Rather than a party that built on the tradition of leaders like Abraham Lincoln and Ronald Reagan, continuing to center principles of liberty and "economic freedom," "The Republican Party of today ... is ignoring self-evident truths about the rule of law and limited government in exchange for self-serving lies," he argued.
The five-term congressman and former prosecutor said that while he was grateful for his time in office, and for voters' support to fight "against the left's policies," he said he worried the GOP in its current state was not a sufficient alternative.
"Americans are rightfully concerned about our nation's future and are looking to Republicans in Washington for a course correction. But their hope for Republicans to take decisive action may be in vain," he said.
"Our nation is on a collision course with reality," he said, "and a steadfast commitment to truth -- even uncomfortable truths -- is the only way forward."
"I made the decision to leave Congress because tough votes are being replaced by social media status," he said, going on to add: "It's time to stop feeding popular narratives and start addressing the long-term solutions."
Buck was not the only notable Republican to announce their plans to leave the House this week. Texas Rep. Kay Granger, chair of the powerful House Appropriations Committee, said in her own statement that she would be leaving Congress after the current term, her 14th.
Granger's vote also drew attention during the speakership fight when she, along with some other moderate and establishment members of the party, blocked Jordan's ascent.
"I have been able to accomplish more in this life than I could have imagined, and I owe it all to my incredible family, staff, friends, and supporters," Granger said in her statement. "The United States of America is the greatest country in the world because of our people and the vision of our Founding Fathers who created a nation that ensures every man, woman and child has the opportunity to succeed."
"I am encouraged by the next generation of leaders in my district," she said. "It's time for the next generation to step up and take the mantle and be a strong and fierce representative for the people."