Sen. Sheldon Whitehouse, D-R.I., believes former national security adviser Mike Flynn might already be cooperating with the Justice Department's investigation by Special Counsel Robert Mueller. But Whitehouse acknowledges there's no proof of that at the moment.

"There is at least a reasonable hypothesis that Mike Flynn is already cooperating with the Department of Justice investigation and perhaps even has been for some time," Whitehouse told CNN. "All the reporting indicates that they've got him on a false statement felony for what he told the FBI when they interviewed him in the White House."

He made those remarks after a week in which Flynn seems to have done little cooperating with either of the two congressional investigations, at least publicly. After Flynn invoked his Fifth Amendment rights in response to an earlier subpoena from the Senate Intelligence Committee, the committee issued two new subpoenas against two of Flynn's businesses.

Also this week, the House Intelligence Committee said they were drafting subpoenas to Flynn and his businesses as well.

Whitehouse's statements seem to show an increasing worry that the appointment of a special counsel now may have cut the congressional investigations out of the loop in meaningful ways.

After senators received a briefing last week from Deputy Attorney General Rod Rosenstein about the appointment of a special counsel, Senator Chris Coons, D-Del., said, "My concern is that we not end up in a place where special counsel doesn't communicate to Congress for months, or years, a decision he's made about the scope of the investigation."

Legislators were also shut out by the Justice Department this week in their attempt to get copies of memos made by former FBI Director James Comey. Those memos allegedly detail conversations between President Trump and Comey, and news reports have indicated that Trump asked Comey to "back off" the investigation against Flynn.

Flynn is a retired Army general, and was a campaign surrogate for Trump in 2016. However, after becoming national security advisor, Flynn was forced to step down because of false statements he made about conversations he had with Russian Ambassador Sergei Kislyak. Flynn has also been under scrutiny for income he accepted from work in Russia and Turkey.

In late March, Flynn offered testimony to both the House and Senate intelligence committees in exchange for immunity, but neither accepted the offer.

A request for comment from Flynn's attorney was not returned.