As I see it, Libby's real problem is he's a bit of a ditz. Good guy, no doubt, but quite frankly if I were Cheney I'd have hired someone a bit slicker. Need someone who's cold as ice in case they are getting grilled - answers need to be factual, but minimalist, and consistent over time.
Correction. Answers need to be, "I don't recall".
You would think that Libby being a high priced lawyer would have done a better job of protecting himself. I guess he who has himself as a client has a fool for a lawyer.