Top Senate Republicans are working hard to prevent the formation of a 9/11-style commission to investigate the Capitol attack, putting the bill’s passage in jeopardy due to concerns about what a high-profile investigation into the events of January 6th might reveal. Mitch McConnell, the Republican Senate minority leader, has stated that he opposes the commission bill in its current form, and several Republicans who previously expressed support have stated that they will no longer support it.

According to a source briefed on the matter, McConnell’s opposition highlights the treacherous path ahead for the legislation, which Senate Democrats could introduce as soon as this week. Republicans have publicly stated their opposition to the creation of a commission for a variety of reasons, including the possibility that it would impede ongoing congressional and Justice Department investigations into the events of 6 January. It has the potential to become politicized. It may make pro-Trump protesters “look bad.”

In the end, McConnell and other top Senate Republicans are concerned that supporting an investigation that is likely to find Donald Trump responsible for inciting the Capitol attack will be used against Republicans in the run-up to the 2022 midterm elections. Both McConnell and House Minority Leader Kevin McCarthy are determined to put Republicans in control of both chambers next year, and both leaders see the commission as a roadblock.

The political calculations looming large echo many of the same concerns raised during the debate over establishing the 9/11 commission, which was opposed by a Bush administration concerned that revealing security lapses would jeopardize their 2004 election chances. However, while lawmakers were able to put months of disagreements aside to form an inquiry – the bill passed in the House with three votes against and by voice vote in the Senate – the Capitol attack has since become just another partisan issue in a divided Congress.

The positions of the two Republican leaders also highlight the fear of what a full accounting of 6 January might reveal about the roles that Republicans may have played in the run-up to the insurgency, potentially inviting unwelcome scrutiny of Trump’s lies about election fraud that they helped spread. Should a 9/11-style commission be appointed, the House minority leader, Kevin McCarthy, in particular, could be left exposed.

McCarthy called Trump as rioters stormed the Capitol, pleading with him to stop them, only for the former president to side with the rioters, saying they appeared to be more concerned with overturning the election results than Republicans in Congress. The mob eventually killed five people while looting the Capitol and looking for politicians, including Vice President Mike Pence.

McCarthy, in desperation, spoke with senior White House advisor and Trump’s son-in-law, Jared Kushner, to try to stop the attack after his pleas to Trump went unanswered, according to a former administration source.

Those conversations between Trump and McCarthy, which addressed the critical question of what Trump was doing and saying privately as the Capitol was overrun, would almost certainly be investigated, raising the possibility that McCarthy himself would have to testify, voluntarily or under subpoena.

McCarthy is also vulnerable to having his own senior aides investigated by a 6 January commission because he hired Brian Jack, the former Trump White House political director who was involved in organizing the “Stop the Steal” rally that preceded the Capitol attack. Zach Wamp, a member of the original 9/11 commission and the former top Republican on the committee overseeing US Capitol police, stated unequivocally that whatever reservations McCarthy or Republicans have about the commission, they must prioritize the country.

The bill to establish a 9/11-style commission passed the House on Wednesday with bipartisan support after 35 Republicans defied McCarthy and an emergency recommendation from the office of the House minority whip, Steve Scalise, to oppose the legislation in a stinging rebuke.

But McConnell’s new opposition – a reversal from his previous support for a commission, as well as his sharp condemnation of Trump for inciting the Capitol attack – reveals the bill’s precarious political situation in the Senate.

In its current form, the bill would require the support of at least ten Senate Republicans before it could be brought to the floor for debate. To overcome an expected filibuster, 10 Senate Republicans would have to cross the aisle and join Democrats.