That's not even the charge that I see. Basically, Libby said one thing happened during the discussion with Russert and Russert said another. Libby was under NO compulsion to tell the truth to Russert.
That's part of the one charge, and I agree that's a weak point of the indictment. He's more likely to get nailed about saying (about his conversation with Russert) "at this point in time I did not recall that I had ever known, and I thought this was something he was telling me that I was first learning." In the light of testimony from numerous individuals who had heard him speaking about Plame earlier, a jury might find that hard to believe.