According to Marc Maron, Rove committed "Treason" by outing "secret agent" Valerie Plame.
As in, the capital offense variety.
Larry O'Donnell says that Karl Rove "outed" CIA "agent" Valerie Plame - the lowest-impact "secret" "agent" of all time.
For those who weren't paying attention, or were getting the story from Atrios (pardon the redundancy), FactCheck.org goes over the "scandal", as does Matt Continetti, while Tim Graham pretty well hammers the media's flightiness on the facts when it comes to this general thread. As to O'Donnell - let's just say that he's kind of a strange fellow in his own right.