Via NBC News:

President Donald Trump’s former national security adviser, retired Gen. Michael Flynn, was subpoenaed by the Senate Intelligence Committee on Wednesday.

The committee, led by Sens. Richard Burr, R-North Carolina, and Mark Warner, D-Virginia, said it requested documents that members believe to be relevant to its investigation into alleged Russian meddling in the 2016 presidential election.

The committee initially requested the documents from Flynn in a letter on April 28, but he declined to comply if he wasn’t offered immunity. The Intelligence Committee declined the deal and has now followed up with an official subpoena.
…
This is the first time the Intelligence Committee has used its subpoena power since the joint inquiry into the terrorist attacks of Sept. 11, 2001, and it’s the first time it has subpoenaed documents since the 1970s, a Senate historian told NBC News.

This is great theater but I’d be shocked if it goes anywhere. Flynn has already been served with a subpoena from the federal grand jury investigating the Russian election interference case… this would be the investigation that everyone claims James Comey was leading in person. If he doesn’t lawyer up and wrap himself in a kevlar version of the Fifth Amendment, he’s a moron.

On the other hand, despite an accomplished career as an intelligence officer, Flynn has shown that he has a self-destructive streak fueled by epic hubris that simply can’t be constrained. He really believes he’s the smartest guy in every room and nothing can disabuse him of that notion. The fact that he has already been interviewed by FBI agents without being advised by counsel probably indicates his goose is thoroughly cooked. I simply can’t imagine a guy who thought he could lie on a security clearance and lie to the Vice President not lying to mere rube FBI agents.

My bet is that he and Carter Page end up in prison. And if they do, Flynn is going to be the ruling psychopath and Page is going to be everyone’s high-strung girlfriend.