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.

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