The House is set to vote on legislation creating an independent commission to investigate the Jan. 6 Capitol attack on Wednesday, with most Republicans expected to vote against the proposal after their leader, Representative Kevin McCarthy of California, said he would not support the bill.
Mr. McCarthy’s opposition to the bill on Tuesday was followed by a statement from his leadership team encouraging a “no” vote. Together, the actions suggested that the House vote would be a mostly partisan affair, highlighting yet again Republicans’ reluctance to grapple with former President Donald J. Trump’s election lies and their determination to deflect attention from the Capitol assault.
Mr. McCarthy had been pushing for any outside investigation to include a look at what he called “political violence” on the left, including by anti-fascists and Black Lives Matter, rather than focus narrowly on the actions of Mr. Trump and his supporters who carried out the riot.
“Given the political misdirections that have marred this process, given the now duplicative and potentially counterproductive nature of this effort, and given the speaker’s shortsighted scope that does not examine interrelated forms of political violence in America, I cannot support this legislation,” Mr. McCarthy said in a statement.
His opposition raised questions about the fate of the commission in the Senate, where Democrats would need at least 10 Republicans to agree to support its formation. Senator Mitch McConnell of Kentucky, the minority leader, said he and other Republican senators were undecided and would “listen to the arguments on whether such a commission is needed.”
But after House Republican leaders initially suggested that they would allow lawmakers to vote however they saw fit, they abruptly reversed course on Tuesday, releasing a “leadership recommendation” urging a “no” vote in an apparent bid to tamp down on the number of members embracing the bill.
In rejecting the commission, Mr. McCarthy essentially threw one of his key deputies, Representative John Katko of New York, under the bus in favor of shielding Mr. Trump and the party from further scrutiny. Mr. Katko had negotiated the makeup and scope of the commission with his Democratic counterpart on the Homeland Security Committee and enthusiastically endorsed it on Friday.
Speaker Nancy Pelosi of California, the Democratic leader, immediately slammed Republican opposition as “cowardice” and released a letter Mr. McCarthy had sent her in February showing that Democrats had incorporated all three of his principal demands for a commission modeled after the one that studied the Sept. 11 terrorist attacks.
In it, Mr. McCarthy said he wanted to ensure any commission had an even ratio of appointees by Republicans and Democrats, shared subpoena power between the two parties’ appointees and did not include any “findings or other predetermined conclusions” in its organizing documents.
Democrats ultimately agreed to all three, but in his statement on Tuesday, Mr. McCarthy said Ms. Pelosi had “refused to negotiate in good faith.”
“I presume Trump doesn’t want this to happen,” said Representative Steny H. Hoyer, Democrat of Maryland and the majority leader. “Enough said.”
Mr. Katko predicted a “healthy” number of Republicans would still vote for it.
“I can’t state this plainly enough: This is about facts,” Mr. Katko told the House Rules Committee at a hearing on the bill. “It’s not about partisan politics.”
But by encouraging Republicans to vote no, Mr. McCarthy positioned the commission as yet another test of loyalty to Mr. Trump, spotlighting a rift within the party between a small minority that is willing to question him and the vast majority that is not.
Senator Chuck Schumer, Democrat of New York and the majority leader, vowed to press the issue with Senate Republicans by quickly bringing the legislation up for a vote in that chamber.
“Republicans can let their constituents know: Are they on the side of truth?” Mr. Schumer said. “Or do they want to cover up for the insurrectionists and Donald Trump?”