WASHINGTON — The Republican Party on Friday officially declared the Jan. 6, 2021, attack on the Capitol and events that led to it “legitimate political discourse,” formally rebuking two lawmakers in the party who have been most outspoken in condemning the deadly riot and the role of Donald J. Trump in spreading the election lies that fueled it.

The Republican National Committee’s overwhelming voice vote to censure Representatives Liz Cheney of Wyoming and Adam Kinzinger of Illinois at its winter meeting in Salt Lake City culminated more than a year of vacillation, which started with party leaders condemning the Capitol attack and Mr. Trump’s conduct, then shifted to downplaying and denying it.

On Friday, the party went further in a resolution slamming Ms. Cheney and Mr. Kinzinger for taking part in the House investigation of the assault, saying they were participating in “persecution of ordinary citizens engaged in legitimate political discourse.”

It was an extraordinary statement about the deadliest attack on the Capitol in 200 years, in which a mob of Mr. Trump’s supporters stormed the complex, brutalizing police officers and sending lawmakers into hiding. Nine people died in connection with the attack and more than 150 officers were injured. The party passed the resolution without discussion and almost without dissent.

The censure marked the latest and most forceful effort by the Republican Party to minimize what happened and the broader attempt by Mr. Trump and his allies to invalidate the results of the 2020 election. In approving it and opting to punish two of its own, Republicans seemed to embrace a position that many of them have only hinted at: that the assault and the actions that preceded it were acceptable.

It came days after Mr. Trump suggested that, if re-elected in 2024, he would consider pardons for those convicted in the Jan. 6 attack and for the first time described his goal as aiming to “overturn” the election results.

For Republicans in Washington, the party’s actions threatened new division as their leaders try to focus attention on what they call the failings of the Biden administration.

Senator Mitt Romney, Republican of Utah, wrote on Twitter, “Shame falls on a party that would censure persons of conscience, who seek truth in the face of vitriol. Honor attaches to Liz Cheney and Adam Kinzinger for seeking truth even when doing so comes at great personal cost.” He did not mention that the party chairwoman who presided over the meeting and orchestrated the censure resolution, Ronna McDaniel, is his niece.

The party’s far-right flank has been agitating to boot Ms. Cheney and Mr. Kinzinger out of the House Republican Conference for months, a push that Representative Kevin McCarthy of California, the minority leader, has tried to brush aside. And their formal censure is sure to stir up those efforts again.

“We need to move on from that whole discussion and, frankly, move forward and get the House back in 2022,” said Representative Mike Garcia, a California Republican facing a difficult re-election campaign in a newly configured district.

Most House Republicans tried to ignore the actions of the party on Friday, refusing to answer questions or saying they had not read the censure resolution. Representative Dan Crenshaw, Republican of Texas, called it “dumb stuff,” while Representative Mark Green, Republican of Tennessee, lamented the distraction from “this abysmal administration’s record.”

Democrats, however, were incensed, especially at the censure resolution’s description of the Capitol attack as “ordinary citizens engaged in legitimate political discourse,” and the ongoing legal investigations of Mr. Trump in New York and Georgia “Democrat abuse of prosecutorial power.”

“The Republican Party is so off the deep end now that they are describing an attempted coup and a deadly insurrection as political expression,” said Representative Jamie Raskin, Democrat of Maryland and a member of the special House committee investigating the Capitol attack. “It is a scandal that historians will be aghast at, to think that a major political party would be denouncing Liz Cheney for standing up for the Constitution and not saying anything about Donald Trump’s involvement in the insurrection.”

Representative Adam Schiff, Democrat of California and who is also on the committee, said, “their party has degenerated into a cult to the former president, unwilling to acknowledge the truth, and I think they condemn themselves with their resolution.”

In his own defense, Mr. Kinzinger said, “I have no regrets about my decision to uphold my oath of office and defend the Constitution. I will continue to focus my efforts on standing for truth and working to fight the political matrix that’s led us to where we find ourselves today.”

The resolution speaks repeatedly of party unity as the goal of censuring the lawmakers. saying the party’s ability to focus on the Biden administration was being “sabotaged” by the “actions and words” of Ms. Cheney and Mr. Kinzinger which indicate “they support Democrat efforts to destroy President Trump more than they support winning back a Republican majority in 2022.”

More practically, the moves of the party in Salt Lake City will make it easier for the Republican apparatus to abandon Ms. Cheney and throw its weight and money behind her main primary challenger, Harriet Hageman.

The censure resolution declares that the party “shall immediately cease any and all support of” both lawmakers “as members of the Republican Party for their behavior which has been destructive to the institution of the U.S. House of Representatives, the Republican Party and our republic, and is inconsistent with the position of the Conference.”

Mr. Kinzinger has already announced he won’t seek re-election, as have several other House Republicans who voted to impeach Mr. Trump for inciting the attack on the Capitol. Ms. Cheney, however, has vowed to stand for re-election.

Earlier this week, the Wyoming delegation to the Republican National Committee submitted a so-called “Rule 11” letter, formalizing party support for Ms. Hageman. The existence of the letter was reported by The Washington Post.

The letter allows the Republican National Committee to send resources to the Wyoming branch of the party to spend on Ms. Hageman’s behalf — essentially designating her as the party’s presumptive nominee. The designations are common in Republican politics, but typically are used to support incumbents who may be facing token primary challengers. Florida’s delegation, for instance, filed a similar letter months ago that allowed the national committee to funnel resources to support the re-election campaigns for Gov. Ron DeSantis and Senator Marco Rubio.

Ms. Cheney, who faces an uphill battle in her re-election bid against a Republican Party aligned with Mr. Trump, said party leaders “have made themselves willing hostages” to Mr. Trump.

“I do not recognize those in my party who have abandoned the Constitution to embrace Donald Trump,” she said. “History will be their judge. I will never stop fighting for our constitutional republic. No matter what.”

Ms. Cheney’s spokesman, Jeremy Adler, condemned the Wyoming G.O.P. leadership and its chairman, Frank Eathorne, for directing resources to Ms. Hageman. Mr. Eathorne did not respond to messages Friday; other members of the Wyoming delegation declined to comment.

“Frank Eathorne and the Republican National Committee are trying to assert their will and take away the voice of the people of Wyoming before a single vote has even been cast,” Mr. Adler said.

Ms. Cheney has a commanding financial advantage over Ms. Hageman, according to federal campaign finance reports released earlier this week. Ms. Cheney entered 2022 with nearly $5 million in campaign cash, while Ms. Hageman reported just $380,000.

The censure resolution was watered down from an initial version that called directly for the House Republican Conference to “expel” Ms. Cheney and Mr. Kinzinger “without delay.” That demand was dropped. However, the language condemning the attack on “legitimate political discourse” was then added.

William J. Palatucci, a Republican National Committee member from New Jersey, said those changes were made “behind closed doors.” The final language was officially circulated to committee members early Friday morning. He called it “cancel culture at its worst.”

“The national committee attacking Liz Cheney is distracting and counterproductive,” he said. “We should be spending our time shooting at Democrats, not Republicans.”