Committee ranking member Sen. Mark Warner (D-VA) talks with committee chairman Sen. Richard Burr (R-NC) during a Senate Intelligence Committee hearing concerning foreign influence operations' use of social media platforms, on Capitol Hill, September 5, 2018 in Washington, DC. (Photo by Drew Angerer/Getty Images)

WASHINGTON — Virginia Sen. Mark Warner’s political legacy could be defined by how he navigates a high-stakes Senate investigation into Russian election meddling.

As the top Democrat on the Senate Intelligence Committee, Warner is working to shepherd through a bipartisan Russia probe in a Congress that’s bitterly divided. That involves maintaining a civil relationship with North Carolina Republican Sen. Richard Burr, the chairman of the committee, even as the panel investigates whether Burr’s ally — President Donald Trump — colluded with the Russians to sway the 2016 U.S. election.

Their work has long been billed as the most bipartisan Russia investigation underway on Capitol Hill, with Burr and Warner consistently espousing their commitment to working across the aisle. If they can stick together to issue joint conclusions, their final report will have far more clout than it would if the parties split on the findings.

Warner, the former Virginia governor who has served in the Senate since 2009, has called himself a “radical centrist.” And he has labeled his work on this investigation “probably the most important thing I’ve done in public life.”

The committee is inching toward issuing its final report, with no firm deadline. It was initially expected to wrap up by the end of 2017, but some observers now predict that it’ll come out after Special Counsel Robert Mueller issues his findings.

And while Warner and Burr have worked to publicly convey their bipartisan bona fides during two years of deliberations that take place largely behind closed doors, a public rift earlier this month hinted at divisions that could threaten their goal of finding common ground.

Burr said in an interview that his committee, which has been investigating election meddling since early 2017, hasn’t found anything suggesting “collusion” between Trump’s campaign and Russia.

Trump amplified Burr’s comments on Twitter, writing, “The Senate Intelligence Committee: THERE IS NO EVIDENCE OF COLLUSION BETWEEN THE TRUMP CAMPAIGN AND RUSSIA!”

Warner fired back in the unusual public spat about the committee’s confidential work. “Respectfully, I disagree,” Warner told CNN, noting that he didn’t want to reach any conclusions until the investigation wrapped up.

That’s not likely to happen for a while.

The committee has interviewed more than 200 witnesses and reviewed more than 300,000 pages of documents, according to a Democratic committee aide. Senators have planned five reports, two of which have already been released. The next — looking at how President Barack Obama’s administration handled the threat — is expected to come out soon, the aide said. Another will look at Russia’s influence campaign on social media.

The most anticipated report is expected to address whether there was collusion between Russia and the Trump campaign. That could prove to be a dicey topic, as evidenced by the recent Burr-Warner divide.

Burr’s remarks came as a surprise because he made them publicly, said the Democratic committee aide, although people weren’t surprised that he held those views. “That does not mean that everything is hunky dory, as it were,” the aide said, but staffers are taking things one step at a time. “The work continues.”

A Burr spokeswoman did not respond to a request for comment for this story.

Warner finds himself in a tough spot, said Max Bergmann, a senior fellow at the Center for American Progress and director of the organization’s Moscow Project. “Warner could attack Burr, but by doing that, he endangers losing the whole investigation.”

Instead, Warner has spent time and energy on aspects of the investigation where “he has the most freedom of movement. … I think Warner’s view is to not throw the baby out with the bath water,” Bergmann added.

“Warner has also been careful that when Burr sort of steps out publicly to defend the president, Warner hits him and tries to pull him back.”

It’s not only the reputations of Warner and Burr that are on the line.

“I think it’s very important that they get it right,” said former Arizona Democratic Sen. Dennis DeConcini, who served as chairman of the Intelligence Committee in the 1990s. “If they don’t get it right, it’ll be a discredit to the entire Senate and the process.”

He pointed to the partisan rift on the House Permanent Select Committee on Intelligence under the leadership of Republican Chairman Devin Nunes. Republicans and Democrats on that committee offered conflicting reports, despite initial calls for bipartisanship.

“The Senate Intelligence Committee historically has not been partisan, where the Judiciary Committee is and has been,” DeConcini said. When he led the intelligence committee from 1993 until 1995, another Virginian, Sen. John Warner, was the top Republican on the panel.

“We got along very well and it was very bipartisan,” DeConcini said. “I never had a meeting that I started without his approval. … If he was late coming, I waited for him. We always had joint briefings.”

DeConcini said Burr’s public comments about collusion appeared to be the first indication that the chairman “didn’t want to cooperate or do it jointly with Warner.”

He added, “I hope that this is just a bump in the road or hiccup.”

Bergmann of the Center for American Progress agreed that the stakes are high for the Senate committee, even if the release of the Mueller report will likely get more attention.

“It helps create a narrative of what happened,” he said, pointing to the committee’s blockbuster 2012 report on CIA torture as an example of how the panel can shed light on topics that are important to Americans.

In regard to the Russia investigation, “having a really detailed, thorough Senate Intelligence investigation that is sort of pulling no punches, I think, is really important,” Bergmann said.