AS LONG as questions have swirled about the Russian plot to influence last year’s presidential election, it has been fair to wonder whether a partisan Congress could be trusted to conduct thorough and evenhanded investigations into this nationally important but politically sensitive matter. Now, there are tangible warning signs that the integrity of the Senate and House inquiries is at risk.

First, The Post reported Friday that Richard Burr (R-N.C.), the chairman of the Senate Select Committee on Intelligence, which is running the Senate’s investigation, had spoken to journalists as part of a White House effort to rebut a New York Times article reporting communications between members of President Trump’s circle and Russian officials. Among other things, this suggested there were discussions with the White House on matters Mr. Burr should be investigating independently.

Then Devin Nunes (R-Calif.), Mr. Burr’s counterpart in the House, went further, making a series of strong statements that suggested his mind is already made up. “We still have not seen any evidence that anyone from the Trump campaign, or any other campaign for that matter, has communicated with the Russian government,” he said Monday. “There is no evidence that I’ve been presented of regular contact with anybody within the Trump campaign.”

Adam Schiff (Calif.), the ranking House Intelligence Committee Democrat, pointed out that Mr. Nunes said this even though the committee had not received any documents or conducted any witness interviews. Mr. Nunes also played down questions about Michael Flynn, suggesting the ousted national security adviser had really done the nation “a big favor” by staying in contact with the Russians. Mr. Nunes seems more interested in pursuing government leaks — “major crimes,” he termed them — which are, at best, a distraction from the issue of a hostile government’s attempt to compromise the U.S. political system.

For the moment, the Senate investigation still appears to have enough credibility to be useful. Democrats on the Senate intelligence panel have vowed to condemn the inquiry if it becomes a whitewash. So has Sen. Marco Rubio (R-Fla.). Sen. Susan Collins (R-Maine) released an encouraging statement on Sunday. For his part, Mr. Burr should refuse to discuss any substantive matter relating to the investigation with the White House, except in the context of formal interviews the panel conducts. He should certainly not agree to serve as a public relations flack for the president on issues relating to the inquiry. Before this episode, Mr. Burr had, behind the scenes and publicly, prepared the committee to conduct a real investigation. He should stick with that more constructive behavior.

Meanwhile, the House Intelligence Committee agreed Monday night to investigate both high-level leaks and any ties between Mr. Trump’s circle and Russia. But, given Mr. Nunes’s comments, along with the already strong disagreements apparent between him and Mr. Schiff, it seems unlikely the House investigation will serve to clarify matters. It would be better to shut down the House inquiry than to pollute the record with a slanted report from a halfhearted investigation, if that is to be the result.