tax issues, like Al Capone..
Shades of using Scooty Libby's "perjury" to convict him for the non-disclosure of Valerie Plame.
Plenty of prosecutable perjury and deliberate misleading testimony in a federal investigation going on in the Fast and Furious, IRSScandal, and Benghazigate cases.
They'd rather chase after Roger Clemens.