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Story highlights

The Department of Justice is actively investigating Russian meddling in the US election

The congressional committees also investigating want to coordinate

(CNN) —  

A growing number of key lawmakers in both parties are calling on Justice Department special counsel Robert Mueller to detail what specifically his Russia investigation is targeting, with one Democratic senator warning bluntly that failing to do so could jeopardize the criminal probe into President Donald Trump’s former national security adviser Michael Flynn.

Sen. Sheldon Whitehouse, the top Democrat on a Judiciary subcommittee, told CNN Thursday that it’s possible Flynn is cooperating with the Justice Department – and that Capitol Hill has not been kept in the loop. He warned that congressional probes that have subpoenaed Flynn for records could undercut Mueller’s investigation if the former national security adviser is secretly working with the Justice Department as part of its broader investigation into possible collusion between Russian officials and Trump associates during the campaign season.

“There is at least a reasonable hypothesis that Mike Flynn is already cooperating with the DOJ investigation and perhaps even has been for some time,” said Whitehouse, a Rhode Island Democrat.

Whitehouse added he had no direct evidence to suggest that Flynn is cooperating with the Justice Department. But he said there is circumstantial evidence to suggest that it could be the case, saying Mueller must immediately detail the situation to “deconflict” with probes on the Hill to “make sure that congressional investigations aren’t inadvertently competing with DOJ criminal investigations.”

Flynn’s attorney declined to comment when asked if his client was cooperating with the Justice Department.

The concerns speak to the mounting tension between the Hill investigation and the inquiry Mueller is now leading. Already, the Senate judiciary committee and House oversight committee have been stonewalled on their requests for documents, particularly for the memos FBI Director James Comey reportedly wrote about his conversations with Trump about the Russia investigation. And leaders of the Senate intelligence committee have asked to meet with Mueller to detail the path ahead.

On Thursday, the FBI declined to provide documents to the oversight committee, saying in a letter that the bureau was undergoing “appropriate consultation” with Mueller. The letter prompted a sharp response from House oversight chairman Jason Chaffetz, who told acting FBI Director Andrew McCabe that the committee’s investigation is “central” to its oversight responsibilities.

“The committee has its own, constitutionally-based prerogative to conduct investigations,” Chaffetz said, laying out a litany of records he wants from the FBI.

Senate Judiciary Chairman Chuck Grassley has grown frustrated that the FBI has not provided his panel with enough key information – and instead provided some of that information to the Senate intelligence committee even though his panel has jurisdiction over the bureau. And he told CNN earlier this week that he was prepared to subpoena the Comey memos if he had to.

“I haven’t made a decision yet,” Grassley said when asked about issuing subpoenas to the Justice Department. “If we have to, I think you’ll have find Democrats willing to do it too.”

Whitehouse, whose Judiciary subcommittee is investigating Russia meddling, said he’s “willing to grant them a little bit of space” to respond to the panel’s requests. “But it’s limited.”

The Rhode Island Democrat said there are number of factors that suggest Flynn is working the Justice Department in its probe. He pointed out that “all reporting indicates they’ve got him dead to rights on a false statement felony” in his private interview with the FBI over his conversations last year with Russian Ambassador Sergey Kislyak. He also noted that Flynn has gone silent and retroactively signed on as a foreign agent to Turkey. And he noted that a federal grand jury has been summoned and has issued subpoenas to Flynn associates.

RELATED: Senate intel issues 2 new subpoenas related to Flynn

“So none of that proves anything but it’s all consistent with the hypothesis that he’s already cooperating,” Whitehouse told CNN.

“But that’s certainly a hypothetical case of a time when we do need need this de-confliction apparatus in place to make sure that congressional investigations aren’t inadvertently competing DOJ criminal investigations.”

Whitehouse added that there’s confusion about the structure of the investigation, including where other key players fall, like senior Justice official Dana Boente, who had been leading the Russia investigation.

“Clarifying that, I think, is also something that Mueller may want to tell us about,” Whitehouse said. “But one way or the other, we need an answer. We need to understand what the structure is.”

RELATED: The many paths from Trump to Russia

The chairman of the Whitehouse’s committee, Republican Sen. Lindsey Graham, has sounded alarms that the Mueller investigation will impede Congress’ separate investigation into Russia.

“The appointment of the special counsel is really taking Congress more out of the loop and diminished our ability to investigate,” Graham said last week.