And during a presidential campaign too. BFD. Last I checked, Flynn is not a criminal defense attorney who specializes in representing witnesses before Congressional panels.
Now that the shoe is on the other foot, he knows that asking for immunity in the midst of a media feeding frenzy is a smart thing. What will be interesting is whether they give him immunity. I don't think they will. If they call Flynn he would have to invoke the 5th because of the FBI investigation and that would obviously be a bad look. That's where the Dems want to take this. They don't want Flynn testifying under an immunity grant because all Flynn's going to do is back up Trump.