Momentum is stalling amid congressional efforts to swiftly investigate the Jan. 6 riot at the U.S. Capitol, threatened by logistical delays and deepening partisan disagreement about the scope of an independent inquiry advocated by Democrats.

After initial House and Senate hearings that scrutinized law enforcement and intelligence failures leading up to the insurrection, the pace of such public sessions has slowed to a halt, as lawmakers struggle to determine their next investigative steps. Meanwhile, a fight between House Speaker Nancy Pelosi (D-Calif.) and her Republican counterparts over the scope of a Sept. 11-style commission has intensified this week after she announced her plan for how it should be structured.

Now, a looming congressional recess is expected to delay resolution on both fronts until mid-April at the soonest — a pause that threatens to undermine the momentum and spirit of cooperation Democrats and Republicans had exhibited immediately after the riot.

In a letter to fellow lawmakers Monday, Pelosi stressed urgency, writing that “we must get to the truth of how the January 6 assault happened, and we must ensure that it cannot happen again.” But the speaker acknowledged that “it is essential that we proceed in a bipartisan way in order to have a respected outcome.”

Rigid political head winds have formed in the weeks since hundreds of demonstrators, a mob summoned to D.C. by President Donald Trump and his supporters, stormed the Capitol in a deadly and failed bid to stop Congress’s certification of the 2020 presidential election. Most Democrats and Republicans, having embraced a spirit of bipartisanship as they grappled with shock from the attack, have returned to their political trenches to argue about Trump’s second impeachment and trial, and heightened security at the Capitol.

Those disputes have cast a pall over leaders’ vow to investigate the insurrection and its significance in the greater context of how the United States responds to such homegrown threats.

Senate Minority Leader Mitch McConnell (R-Ky.) has complained that Pelosi’s proposed commission has too “narrow” a focus on domestic violent extremist groups such as white supremacists. Republicans, he has said, want the independent group to look at “political violence” more broadly — a position that reflects uneasiness in the GOP with agreeing to scrutinize the pro-Trump, anti-government groups that stormed the Capitol without also examining left-wing extremists who participated in racial justice demonstrations that turned violent last summer.

Many Republicans question whether a Sept. 11-style commission would be useful at all.

“I think the better way to do it right now would be for the committees to continue to work on it and try to come to quicker conclusions,” Sen. Roy Blunt (Mo.), the ranking Republican on the Senate Rules Committee, told reporters.

But that work has been receding from public view. The last public hearings dedicated to the Capitol riot took place on March 5, as Congress turned its attention to finalizing a pandemic-relief stimulus package, and the Senate resumed confirming members of President Biden’s Cabinet. Now only days remain before both chambers are expected to depart Washington for multiweek breaks.

Panel leaders maintain that even if lawmakers are departing Washington, staff-driven, behind-the-scenes investigative work continues.

“Over the course of two productive, bipartisan hearings with federal and Capitol complex security officials, we learned that there were significant failures before and on January 6 . . . which is why we continue to work in a bipartisan fashion to address the necessary reforms to ensure events like January 6 never happen again,” Sens. Gary Peters (D-Mich.) and Rob Portman (R-Ohio), the chair and ranking member of the Senate Homeland Security and Governmental Affairs Committee, said in a joint statement Tuesday evening. “The investigation is ongoing and our findings will be made public at the appropriate time.”

Peters’s and Portman’s panel has been working in partnership with the Senate Rules Committee, and together they have issued requests for documents and other evidence to 22 government agencies. Some of those materials are still incoming, and all of them must be sorted through, according to aides who spoke on the condition of anonymity to be candid about the joint investigation. The lawmakers intend to question additional witnesses privately, they noted.

“If we do that, I don’t know that we lose a lot,” said Blunt, adding, however, his belief that the public “would be reassured if we were, whatever we do, doing it in a visible and very well-understood way.”

The former chief of the Capitol Police and its current acting chief, the former House and Senate sergeants-at-arms, and senior FBI and National Guard officials have testified about the intelligence and communications failures that worsened their response to the riot. But despite bipartisan appeals, the panels’ Democratic chairs have not called for testimony from the former Pentagon officials — including Trump’s Army secretary, Ryan McCarthy, and his acting defense secretary, Christopher Miller — who could clarify why it took so long for National Guard troops to be deployed.

There are no plans for when those officials might be added to the public hearing schedule, which has particularly rankled panel Republicans.

Now, the committees’ work is becoming muddled in a greater political debate about the current state of security at the Capitol.

Last week, Blunt was one of five top-ranking Republican senators to decry the fencing and National Guard troops that continue to form an imposing perimeter around the Capitol grounds. Elsewhere in the GOP, more incendiary lawmakers have taken to referring to the fenced-off complex as “Fort Pelosi.

That criticism came just days after retired Army Lt. Gen. Russel Honoré issued recommendations for improving the intelligence expertise and manpower of the Capitol’s security forces, work that is likely to inform an emergency supplemental appropriations package to pay for improvements.

On Monday, the House sergeant-at-arms announced that the Capitol Police will begin removing portions of the fencing later this month.