WASHINGTON — The political fight over Special Counsel Robert Mueller’s investigation is expected to explode next week when lawmakers reconvene on Capitol Hill for the first time since the public release of the report.

As the partisan caterwauling continues over what Congress should do next, two low-key senators will be leading discussions behind closed doors about how their own report should move forward.

Sens. Richard Burr of North Carolina and Mark Warner of Virginia – the chairman and ranking member of the Senate Select Committee on Intelligence – have been working largely behind the scenes on their own investigation into Russian election interference.

Their collaboration has been billed as an effort that’s remained largely bipartisan on a topic and in a political climate where work across the aisle is exceedingly rare. But a rift between Burr and Warner that spilled into public view earlier this year could deepen as lawmakers spar over Mueller’s public finding and as Democrats demand answers from Burr about new revelations about his communication with the White House about the FBI’s investigations.

Warner laid out his hopes for the Senate’s next steps in an op-ed published Thursday in USA Today, demanding that Congress investigate Mueller’s “sobering findings regarding the president’s attempts to obstruct justice.”

Warner wrote: “The special counsel’s investigation now confronts us with an important choice. We can overlook the president’s morally outrageous behavior; we can ignore the deep deficiencies in our laws and our defenses against foreign interference; or we can do everything in our power to make sure that what happened in 2016 can never happen again.”

Burr, on the other hand, has been cautious in his comments about the president. In a statement issued the day the Mueller report was released, the North Carolina senator didn’t mention Trump.

“I am reviewing Special Counsel Mueller’s report carefully. Furthermore, I look forward to presenting the American people with an accounting of the facts the Committee has uncovered as we conclude our own investigation,” Burr said. “It is my hope to release the first of our final reports in the coming weeks.”

Burr’s office did not respond to requests for comment about whether he plans to ask Mueller to testify before his committee, or whether the report raises new issues that the committee intends to pursue.

The Mueller report revealed that Burr apparently supplied the White House counsel’s office with information about FBI investigations into Russian interference in the 2016 election, Politico reported.

Burr’s spokeswoman, Caitlin Carroll, told Politico that the senator “does not recall this specific conversation with then-White House counsel Don McGahn in March of 2017, but that “any conversations between the two would have been in reference to the need for White House personnel to voluntarily comply with the Senate Intelligence Committee’s Russia investigation.”

A Democratic committee aide said the status of the investigation has been largely unchanged by the release of the Mueller report, although it’s a little easier to say with confidence that the Senate report will wrap up by the end of this year. The end of Mueller’s investigation could make it easier for the committee to get access to witnesses.

Warner issued a statement last week calling it “essential that Congress hear directly” from Mueller regarding his investigation. “The Senate Intelligence Committee continues its own investigation, and I expect to receive a full briefing, an unredacted report, and all the materials underlying the Special Counsel’s findings,” Warner said.

Warner’s office declined to comment on the revelations about Burr’s communications with the White House that were revealed in Mueller’s report.

But some think those revelations threaten the integrity of the Senate investigation.

“Burr has a lot of explaining to do,” said Max Bergmann, a senior fellow at the Center for American Progress and director of CAP Action Fund’s Moscow Project.

“I think it should be embarrassing to Burr that he is highlighted in the Mueller report as someone who is working in cahoots with the White House when he’s supposed to be investigating. It does really cast a shadow on him and his stewardship of the investigation.” Recent editorials in Burr’s hometown newspaper, the Winston-Salem Journal (“Burr failed us”) and the Fayetteville Observer (“What happened, Sen. Burr?”), among others, have voiced a similar sentiment.

Some still have high hopes that the Senate can maintain its bipartisanship as it prepares to issue its final report. Lawmakers on the House Intelligence Committee split last year on their investigation, with Republicans determining there was no evidence of collusion with the Trump campaign.

Keeping Senate lawmakers united will be important both for the public and for the integrity of the institution, said former Arizona Democratic Sen. Dennis DeConcini, who served as chairman of the Intelligence Committee in the 1990s.

Burr has been in a tough political spot leading an investigation that’s raised hackles of the president and the GOP, DeConcini said, adding that he’s impressed that Burr has maintained what appears to be bipartisan support for the Senate probe.

“There’s a long history of senators going on the Intelligence Committee and truly putting their obligation of doing this for the country above whatever the political system is,” the former chairman said. “I truly hope for the country and for the Senate too that [Burr] can maintain that.”

Given Burr’s appearance in the Mueller report, Warner may now have “a greater degree of leverage to pursue a less constrained investigation,” Bergmann said.

“I think any constraints that Burr has put on the investigation now will look even more nefarious after the Mueller report. I think it’s in Burr’s interest to make it as full-fledged an investigation as possible,” he added.

While the committee’s report isn’t likely to be “greeted with the kind of Superbowl-like frenzy” that met the Mueller investigation, Bergmann said, “if it’s got Mark Warner’s imprimatur on it, I think it will be really embraced as an additional important document.”