Ed Koch asks a good question:
Would anyone, particularly someone in high government office with an exemplary record of public service and admittedly a high achiever under these circumstances, lie, deliberately misstate the facts where his testimony would be refuted by a popular television personality certain to be asked? It defies common sense. If he were deliberately lying, he would have said, "I can't recall," or "I think it was Tim Russert," leaving the opportunity to admit error, and in neither case could he, I believe, have been indicted and convicted.
Scooter Libby said he heard Valerie Plame's name from Tim Russert. Russert's recollection is that he did not reveal the name. Libby is convicted, while nothing happened to Russert. Interestingly enough, revealing the name of Valerie Plame was not, in fact, a crime in the first place.