On Wednesday, Richard Burr and Mark Warner, the two leaders of the Senate Intelligence Committee, the body that is widely considered to be the most likely to produce a bipartisan report about Russia and Donald Trump, gave a press briefing on their work.

Their presentation made clear why many in Washington hold out some hope that the Senate Intelligence Committee will produce a report that will give a full picture of Russia’s influence campaign in the 2016 Presidential election. In recent decades, there have been very few congressional investigations affecting a sitting President that don’t descend into partisan combat, with one side working as a defense lawyer for the President and the other acting as an overzealous prosecutor. That’s not to say that partisan investigations don’t ever uncover important facts—partisan investigations from Iran-Contra to Whitewater to Benghazi added crucial information to the public record—but, unlike in a courtroom, there’s no judge or jury to decide the case, and the public is often left confused about the over-all conclusions.

This was always one of the greatest dangers of leaving the Russia probe up to the current investigative machinery in Congress. Unlike the 9/11 Commission, which produced a well-respected consensus report, congressional committees often produce a majority report and a minority report that only serve as fodder for endless partisan debates. The House Intelligence Committee’s Russia investigation succumbed to this dynamic earlier this year when it became clear in open hearings that some Republicans, including the chairman of the committee, Devin Nunes, only cared about protecting Donald Trump, while some Democrats, like Jackie Speier, were willing to publicize spurious conspiracy theories.

The Senate panel has operated differently. Burr, the Republican chairman, cannot be accused of working simply to protect Trump. As he made clear yesterday, he has repeatedly been willing to expand the mandate of the investigation when new information came forward. In January, when it started, the probe was limited to three areas: an evaluation of the Intelligence Community’s report on Russian interference, collusion between either campaign and the Russians, and any ongoing Russian meddling. As the committee interviewed witnesses (more than a hundred) and collected documents (some hundred thousand pages) it also looked at the Obama Administration’s response to the Russian cyber campaign; the details of a meeting between Trump campaign officials and the Russian Ambassador to the U.S. at the Mayflower Hotel, on April 27, 2016; changes to the Republican Party’s 2016 platform that relaxed the G.O.P.’s previously hawkish stance toward Russia; some aspects of Trump’s firing of the F.B.I. director, James Comey, although Burr made it clear that this was more of an issue for the special counsel Robert Mueller; the meeting at Trump Tower between a Russian lawyer and Trump’s campaign leadership; the Trump Organization’s interest in a building project in Moscow while Trump was running for President; Russia’s use of paid political ads on social-media platforms such as Facebook; and the Trump dossier put together by Christopher Steele, the former British spy who, Burr noted with some frustration, has refused to assist the committee.

Burr asked the public to take him at his word when he said that he would allow the facts to define the contours of the investigation, and so far he has lived up to that promise. But this is also the most serious problem with Burr and Warner’s investigation: we are being asked to take them at their word. The investigation has been shrouded in secrecy, and Warner and Burr, while demonstrating a reassuring united front of bipartisanship, have operated with an enormous degree of seclusion. Burr actually bragged about the lack of transparency.

“We don’t release documents provided to our committee, period,” he scolded reporters who wondered if he would release the Facebook ads the Russians bought. “Let me say it again. The Senate Intelligence Committee does not release documents provided by witnesses.” He added, “I want you to know that you only see glimpses of the amount of work the committee has done. We’re doing much of our work behind closed doors to insure the privacy and the protection of witnesses and sensitive sources and methods.”

More important, Burr and Warner have made claims about highly contentious issues without offering any public backup. Burr has given short updates on various areas of the investigation, and made it clear that the committee has not come to any conclusions about collusion between the Trump campaign and the Russians. He noted that the committee will likely endorse the conclusions of the American intelligence community’s Russia report. In most areas he discussed, he didn’t offer any conclusions. But there was one notable exception. He said that the Senate Intelligence Committee had finished its investigation of the pro-Russia changes by the G.O.P.’s platform committee after interviewing every person who might have information about the episode. “Campaign staff was attempting to implement what they believed to be guidance to be a strong ally on Ukraine, but also leave the door open for better relations with Russia,” he said. “I’m giving you the feedback we got from the individuals who were in the room making the decisions.” This was a highly exculpatory comment about one of the central mysteries in the Russia story, made without a single piece of supporting evidence. The interviews were all conducted in secret, and, if any documents were produced to help understand the episode, we don’t know about them.

This lack of transparency is probably the inevitable by-product of leaving the investigation of an act of war against the United States to a narrow congressional committee that is used to operating in secret. In fairness to Burr and Warner, there does need to be some level of privacy to secure information from some witnesses, and some level of security to review classified material. And Burr did promise that “at the end of this process, we will be sure that we present to the American people our findings as best as we have been able to accumulate them.” But so far the committee has been so secretive and so unwilling to give the public a glimpse of its work that it risks undermining whatever conclusions it ultimately presents. Burr noted that the investigation he once hoped to complete by the end of the year may spill into 2018. It’s not too late for him and Warner to change course.