WASHINGTON — A sharply divided House voted on Wednesday to create an independent commission to investigate the Jan. 6 Capitol assault, overcoming opposition from Republicans determined to stop a high-profile accounting of the deadly pro-Trump riot.
But even as the legislation passed the House, top Republicans locked arms in an effort to doom it in the Senate and shield former President Donald J. Trump and their party from new scrutiny of their roles in the events of that day.
The 252-to-175 vote in the House, with four-fifths of Republicans opposed, pointed to the difficult path for the proposal in the Senate. Thirty-five Republicans bucked their leadership to back the bill.
The vote came hours after Senator Mitch McConnell of Kentucky, the Republican leader, declared his opposition to the plan. Mr. McConnell had said just a day earlier that he was open to voting for it, and he had previously been vocal both in condemning Mr. Trump’s role in instigating the assault and denouncing the effort by some Republicans on Jan. 6 to block certification of the 2020 election results.
His reversal reflected broader efforts by the party to put the assault on the Capitol behind them politically — or to recast the rioting as a largely peaceful protest — under pressure from Mr. Trump and because of concerns about the issue dogging them into the 2022 midterm elections.
Proponents hailed the move to establish the commission as an ethical and practical necessity to fully understand the most violent attack on Congress in two centuries and the election lies by Mr. Trump that fueled it. Modeled after the body that studied the Sept. 11, 2001, attacks, the 10-person commission would take an inquiry out of the halls of Congress and deliver findings by Dec. 31.
“I was on the Capitol floor, the speaker was in the chair and a howling mob attacked the United States Capitol,” Representative Zoe Lofgren, Democrat of California and the chairwoman of a committee already studying the attack, said in an animated appeal before the vote. She reminded colleagues of the “pounding on the doors” and the “maimed police officers.”
“We need to get to the bottom of this to not just understand what happened leading up to the Sixth, but how to prevent that from happening again — how to protect the oldest democracy in the world in the future,” Ms. Lofgren said.
But the prospects for Senate passage dimmed substantially after Mr. McConnell joined his House counterpart, Representative Kevin McCarthy of California, and Mr. Trump in panning the proposal drafted by Democrats and a moderate House Republican as overly partisan and duplicative of continuing Justice Department criminal prosecutions and narrow congressional investigations.
“After careful consideration, I’ve made the decision to oppose the House Democrats’ slanted and unbalanced proposal for another commission to study the events of Jan. 6,” Mr. McConnell said on the Senate floor.
Many rank-and-file Republican senators who had flirted with backing the commission idea quickly fell in line, as well, arguing that the proposal was not truly bipartisan and that the investigation would take too long and learn too little. Their positions made it less likely that Democrats could win over the 10 Republican votes they would need to reach the 60-vote threshold required for passage of the bill in the evenly divided Senate.
Republican leaders, who witnessed the events of Jan. 6 and fled for their lives as an armed mob overtook their workplace, had briefly considered supporting the commission out of a sense of fairness. The 9/11 commission was adopted nearly unanimously two decades ago, and its work was widely heralded.
Their final opposition pointed to a colder political calculation now driving Republicans’ approach to 2022: that it is better to avoid a potentially uncontrollable reckoning centered on Mr. Trump and the false claims of voter fraud he continues to promulgate.
“I want our midterm message to be about the kinds of issues that the American people are dealing with — it’s jobs and wages and the economy, national security, safe streets, strong borders and those types of issues,” said Senator John Thune of South Dakota, Mr. McConnell’s No. 2. “Not relitigating the 2020 election.”
Coming after a bipartisan negotiation that had been sanctioned by Mr. McCarthy, the outcome was dispiriting to those who felt that Mr. Trump’s exit from the public stage and the realities of an attack on the seat of government might help ease the strained relations between Republicans and Democrats.
The two parties are expected to deadlock again on Thursday when Democrats call a vote on a $1.9 billion spending plan to harden the Capitol’s defenses four months after at least five people died in connection with the invasion, which also injured nearly 140 people and caused tens of millions of dollars in damage to the Capitol complex.
Democrats were furious. They had agreed to several concessions to Mr. McCarthy under the belief he would support the deal, only to see him slam it publicly because it did not study unrelated “political violence” on the left. Some Democrats said the episode only underscored to them that it was pointless to negotiate with the Republicans on any of the big issues that divide the parties, including President Biden’s infrastructure proposal.
In the House, Democratic leaders threatened to pursue a more partisan investigation of Jan. 6 through existing congressional committees or by creating a new select committee if the commission proposal dies.
Democratic lawmakers, and even some Republicans, speculated that Mr. McCarthy’s reticence could have been driven in part by an effort to prevent damaging information about his own conversations with Mr. Trump around Jan. 6 from coming to light at a time when he is trying to help his party retake the House and become speaker.
“You’ll have to ask them what they are afraid of,” Speaker Nancy Pelosi of California told reporters. “But it sounds like they are afraid of the truth, and that is most unfortunate.”
Senator Chuck Schumer, Democrat of New York and the majority leader, vowed to call a vote on the Senate floor in the coming weeks to force Republicans to take a public position, though he did not offer a specific date.
“The American people will see for themselves whether our Republican friends stand on the side of truth or on the side of Donald Trump’s big lie,” he said.
During debate on the House floor, Republicans who supported the panel repeatedly sought to frame it as a reprise of the 9/11 commission, whose leaders endorsed the new effort. Though the Senate impeachment trial and a handful of congressional committees have already produced a detailed account of that day, key questions remain unanswered, particularly about Mr. Trump’s conduct and the roots of intelligence and security failures.
“Make no mistake about it, this is about facts, it’s not partisan politics,” said Representative John Katko, Republican of New York, who negotiated the legislation creating the commission with Representative Bennie Thompson, Democrat of Mississippi.
“Jan. 6 is going to haunt this institution for a long, long time,” said Representative Fred Upton of Michigan, another Republican who voted in favor of establishing the commission. “Five months later, we still don’t have answers to the basic questions: who knew what when, and what did they do about it?”
Among the Republicans voting in favor of the commission were a familiar group of moderates and stalwart critics of Mr. Trump, many of whom either voted to impeach him over the Jan. 6 attack or otherwise condemned his actions. The most notable was Representative Liz Cheney of Wyoming, who was run out of the party leadership last week because she refused to stop criticizing Mr. Trump for his attempts to overturn the election.
But supporters also counted a wider cast of established Republicans from conservative-leaning districts who, despite the politics, were rattled by the attack and want a thorough study.
Among those voting no was Representative Greg Pence, Republican of Indiana and the brother of former Vice President Mike Pence, whose opposition to blocking certification of the election results made him one of the principal targets of the pro-Trump rioters, some of whom erected a gallows outside the Capitol. In a statement, Representative Pence said Ms. Pelosi was trying to appoint herself “hanging judge” to carry out a “predetermined political execution of Donald Trump.”
The level of Republican defections on Wednesday’s vote was embarrassing for Mr. McCarthy at a time when he has vowed to unite the party, and few Republicans were willing to defend their opposition during debate. Allies of Mr. Katko were particularly incensed that the minority leader deputized him to make a deal and then cut him loose when he did.
Democrats sought to further embarrass Republicans by circulating an unusual letter by Capitol Police officers expressing “profound disappointment” with Mr. McCarthy and Mr. McConnell.
“It is unconscionable to even think anyone could suggest we need to move forward and get over it,” the officers wrote in the unsigned letter.
In the Senate, a small group of moderate Republicans suggested on Wednesday they were still interested in pursuing a commission, albeit with changes to how staff members would be appointed. But Mr. McConnell left very little possibility that his leadership team could get to yes.
Mr. McConnell had emerged from Jan. 6 as one of Mr. Trump’s most outspoken Republican critics, pinning blame squarely on him for losing the House, Senate and White House and inspiring the most deadly attack on Congress in 200 years. But in the months since, as Mr. Trump has reasserted control over the party, Mr. McConnell has been increasingly reluctant to stir his ire.
On Wednesday, he insisted that he believed in getting to the bottom of what happened, but he argued that investigations already underway by the Justice Department and bipartisan Senate committees were sufficient. In reality, the scope of that work is likely to be much narrower than what a commission could study.
“The facts have come out,” Mr. McConnell said, “and they will continue to come out.”