("Denny Crane: Gun Control? For Communists. She's a liberal. Can't hunt.")
I wonder if there is a credible angle of defense (not that I am endorsing such a defense or implying its accuracy, just theorizing) for Libby that goes like this:
It became clear early in this investigation that one or more persons within the investigation or grand jury was illegally leaking secret testimony. Because much of the matter involved highly sensitive information, he chose to mislead the GJ/investigation to head off a line of inquiry that would have gotten into areas that could not be allowed to leak out without endangering national security.
I would guess the odds of legal success of such an excuse would be lower than the odds of political success, but it does seem that many of the leaks going back months and months were quite accurate.