Heading into a late Wednesday vote, congressional Republicans are divided over whether to support the creation of an independent commission tasked with investigating the Jan. 6 attack on the Capitol as the party faces another moment of reckoning over the falsehoods President Donald Trump spread about the election and his role in the riot.

House Minority Leader Kevin McCarthy (R-Calif.) on Tuesday announced his opposition to a bipartisan deal to establish a panel divided equally between Republican and Democratic appointees, arguing that the commission should be looking into other acts of politically charged violence, as well. He charged that the proposal, which will be voted upon Wednesday, was “shortsighted,” “duplicative” and “potentially counterproductive,” focusing his blame on Speaker Nancy Pelosi (D-Calif.), despite the fact that several Republicans — including the top GOP member of the House Homeland Security Committee — have endorsed the measure.

But in a striking break between party leaders, Senate Minority Leader Mitch McConnell (R-Ky.) said that the Senate GOP is “undecided” about whether to back the commission and is “willing to listen” to arguments in favor of the panel.

“We want to read the fine print,” McConnell told reporters. “If the majority leader puts it on the floor, we will react accordingly.”

Senate Majority Leader Charles E. Schumer (D-N.Y.) said Tuesday that he would bring the legislation up for a vote.

McConnell caveated his comments and said the two issues being scrutinized by Senate Republicans are whether the commission would potentially interfere with law enforcement efforts to identify and prosecute people who took part in the attack, and whether it is set up to allow for a bipartisan investigation, particularly based on how staff would be chosen.

He noted that “hundreds of arrests” had already been made in relation to the Jan. 6 assault, in which approximately 10,000 people laid siege to the Capitol and about 800 broke inside, vandalizing the building as they searched for lawmakers, including Pelosi and Vice President Mike Pence.

But the fact that McConnell left the door open to backing the commission after consulting with his rank and file suggests there may be enough Republican votes to pass the legislation in that chamber.

Several Republicans, including some who voted this year to convict Trump on impeachment charges for inciting the insurrection, indicated this week that they are open to backing a commission. Sen. Mike Rounds (S.D.), who did not back Trump’s impeachment, told NBC News on Tuesday that he was for a commission because “I don’t want it to be swept under any rug.”

In the House, the Republican coalition supporting a commission had expanded beyond those who voted for Trump’s second impeachment, as well.

“Right now I’d like to vote for it,” said Rep. Don Bacon (R-Neb.), who opposed impeachment and has become a top target for Democrats trying to flip seats in 2022. “I don’t mind having transparency and putting a spotlight on what happened — I think it’s all right.”

The bipartisan Problem Solvers Caucus endorsed the bill Tuesday, meaning that many of its 29 Republican members could vote to create the commission.

In a sign that House GOP leaders are nervous about how many of their members will vote for the bill, House Minority Whip Steve Scalise (R-La.) sent a missive out to the GOP conference late Tuesday, telling them that “leadership recommends a NO vote.” His message came after leaders had earlier said they didn’t plan to whip the vote and would let members vote how they wanted.

Pelosi is expected to have more than enough support to pass the commission legislation as well as a supplemental spending bill to pay for improvements to Capitol security, when it comes to a vote this week.

But the commission vote will be a litmus test for how willing Republicans are to dissociate themselves from Trump’s lingering shadow over party politics and risk his wrath.

He denounced the bill Tuesday night.

“Republicans in the House and Senate should not approve the Democrat trap of the January 6 Commission. It is just more partisan unfairness and unless the murders, riots, and fire bombings in Portland, Minneapolis, Seattle, Chicago, and New York are also going to be studied, this discussion should be ended immediately,” Trump said in a statement. “Republicans must get much tougher and much smarter, and stop being used by the Radical Left. Hopefully, Mitch McConnell and Kevin McCarthy are listening!”

While Trump is opposed to an independent Jan. 6 commission, he has not gotten directly involved in McCarthy’s efforts to block it, according a person who has spoken directly to him about the matter, who like others spoke on the condition of anonymity to describe private conversations.

The former president has complained that law enforcement has been more vigorous in dealing with rioters Jan. 6 than they were during racial justice protests last summer, according to these people.

A spokesman for Pence did not respond to a request for comment on whether he supports a commission.

Among the potential evidence that could be turned up by the commission is testimony about phone calls between Trump and Republicans where he was asked to do something to stop the attack.

Trump has privately conceded that the Jan. 6 riot was bad but does not want to say it publicly for fear it will drawing more public criticism — and that his opponents might use the commission to attack him, according to people familiar with his views.

House Homeland Security Committee Chairman Rep. Bennie Thompson (D-Miss.), who drafted the bipartisan commission legislation with the committee’s top Republican, Rep. John Katko (N.Y.), said on CNN over the weekend that if a commission is established, Trump should be called to testify.

The legislation gives the proposed 10-member commission the power to subpoena witnesses on a bipartisan basis. Five commissioners, including the chair, would be appointed by Democratic congressional leaders, while five, including the vice chair, would be chosen by Republican congressional leaders.

The commission could also force McCarthy to detail his conversations with Trump and others at the White House regarding the attack on the Capitol. During the impeachment trial, it emerged that on Jan. 6, shortly after the mob had broken inside, Trump had rebuffed McCarthy’s pleas to call off his supporters, telling him, “Well, Kevin, I guess these people are more upset about the election than you are.”

McCarthy deputized Katko to negotiate with Thompson, after discussions with Pelosi on an earlier draft commission broke down this spring over disputes regarding its composition and scope. Democrats wanted to focus the investigation on the right-wing groups that promoted the Jan. 6 demonstrations, while Republicans demanded the panel cast a wider net and consider left-wing extremism as well.

Katko, who voted to impeach Trump in January, had been a co-author of the GOP alternative to Pelosi’s initial bill. But after weeks of negotiating with Thompson, he backed a bipartisan deal exclusively focused on Jan. 6, calling it “a solid, fair agreement that is a dramatic improvement over previous proposals.”

McCarthy, however, rejected it out of hand, and during a private House GOP meeting Tuesday, urged others to vote against it.

“Thanks for not throwing me under the bus, Kevin,” Katko said in response, according to a Republican aide.

McCarthy, despite condemning Trump for the riot early on, has since sided with Republican lawmakers eager to stamp out high-level scrutiny of the event. Last week, he backed a campaign to oust Rep. Liz Cheney (R-Wyo.) from her House GOP leadership post, over her continuing effort to challenge Trump’s false claims that the 2020 election was stolen and her support for the commission.

Some of the GOP lawmakers who campaigned for Cheney’s ouster have been railing against the bipartisan commission deal with equal vitriol.

“The Jan 6th Commission is just another big smokescreen and witch hunt on Trump and his supporters to fuel the hate, while ignoring Antifa/BLM nonstop violence,” Rep. Marjorie Taylor Greene (R-Ga.) tweeted Tuesday. “It will be used by the media to distract people away from the real damage Biden and Dems are doing to the country.”

The Biden administration voiced its support for the commission deal Tuesday, arguing the nation deserves “a full and fair accounting” to prevent future violence and strengthen Democratic institutions. The White House also voiced support for the $1.9 billion spending bill to make security improvements to the Capitol.

McCarthy’s effort to cater to the pro-Trump voices in his party has been viewed by many as a play to hold on to the House’s top Republican spot, in the hopes that the GOP might wrest back majority control of the chamber in the 2022 midterm elections. Trump is expected to play an influential role in those contests.

But McCarthy’s rejection of the deal Katko struck — after having previously blessed his efforts — has rankled others in the party. Some speculated that it might drive rank-and-file GOP members otherwise on the fence over whether to support the commission, to show solidarity with Katko.

After this week’s House vote, the commission must still earn the Senate’s endorsement before Biden can sign it into law. The chances of the bill getting through the 50-50 split Senate may depend in large part on how strong a mandate it gets from House Republicans. On Tuesday, many appeared torn over what to do.

“I’ve been calling for a bipartisan commission. . . . I just would like to have a better knowledge of who’s going to be on the commission,” Rep. James Comer (Ky.), the top Republican on the House Committee on Oversight and Reform, told reporters. Comer previously worked with Katko and top House Administration Committee Republican Rep. Rodney Davis (Ill.) on the GOP’s alternative proposal for an independent commission.

Comer complained that the Democratic-led House was “rushing it through” before members have all the details they need.

“I didn’t say I was a no vote,” he added. “I haven’t decided yet.”

At this point, the commission legislation is expected to get heftier bipartisan backing from the House than the supplemental spending bill that will be on the floor this week. That legislation will then also have to go to the Senate, where it will probably undergo some changes.

The $1.9 billion dollar measure seeks to pay for improvements to equipment and training, enhanced security details for members, and settle debts with the Capitol and D.C. police, the National Guard and various other government agencies for their response to the Jan. 6 insurrection. But congressional Republicans are balking at some of the proposals within the House Democratic-written legislation, such as $200 million for a “quick reaction force” within the National Guard to augment the Capitol Police response to emergencies.

How far the parties are willing to go in the Senate — where 60 votes are necessary to avoid procedural roadblocks — may become evident when the chamber’s Rules, and Homeland Security and Governmental Affairs panels release a highly anticipated interim report detailing an analysis of the Jan. 6 security lapses and recommendations for how to improve them. The bipartisan report is being released as soon as next week in part to inform the Senate debate surrounding the supplemental spending legislation, according to people familiar with the panels’ plans.

John Wagner and Paul Kane contributed to this report.