I think materiality is the issue that most bothers me.
Fitz knew who the leaker was as he entered this case. He knew it was Armitage. He also knew that Plame was not a covert agent per the law on that issue. He knew no crime had been committed.
At that point, the case should have been stopped.
However, assuming the worse about Libby for a moment. Assume Libby did not know who the culprit was. However, Libby would have known it was not himself. His actions would then be taken to assure that someone did not FALSELY conclude that it was him.
He is asked "when did you first tell that Plame was an agent?" If he had told at week #1 to one person and also told at month #1 to another person, why did he place himself in his testimony to the FBI in the later incident? Perhaps to place himself further from the time of the incident itself. Perhaps he saw greater distance in time as being safer.
All along, Libby knows that Libby is not the one who outed Plame. What did he fear happening if he placed himself closer in time? I'd say he feared some kind of false accusation by an overzealous prosecutor.
At this point, what is his crime? He is guilty of lying to the FBI and the Grand Jury in an effort to distance himself from a crime that he is certain that he did not commit AND that the prosecutor will know that Libby did not commit.
He would have been far better off, now that we know Armitage's name, never to have spoken to the FBI or the Grand Jury beyond a pleading of the 5th Amendment.
From henceforth, I will never suggest otherwise to anyone who has to speak to authorities.
As for Libby, if we assume he lied to the FBI/Grand Jury, then he deserves some form of punishment. That punishment should be a wristslap since he is clearly innocent and has been known all along to be innocent. I'd give him a suspended sentence with lots of community service.
If I were on the jury, and if I had been permitted to consider that there was no crime committed and that it was definitely not committed by Libby, then I would have nullified this case. If they had had all the above information and Andrea Mitchell's testimony that disputed Russert's testimony, then I could not have convicted him.
Obstruction of justice does not require another crime be committed. All it requires is that he knowingly impede the functioning of a grand jury by misleading it. By lying to the grand jury about when he learned of Ms. Wilson's identity and the sum and substance of his conversations about Ms. Wilson to reporters, he obstructed justice. It is irrelevant that he was not the actual source of the leak (Mr. Armitage, who cooperated with investigators), nor is is relevant if Ms. Plame was or was not covert. What matters is only that he lied to the grand jury and investigators.
Remember - no crime need be committed for a grand jury to exist. There must only be reason to believe a crime may have been committed. Grand juries are investigatory tools, not fact-finders.
I have absolutely no sympathy for Libby. I didn't buy the "I forgot" defense (come on - one of the sharpest Beltway lawyers "forgot"? Not bloody likely.) My support for the Iraq war does not extend so far as to give immunity to lawyers for lying to grand juries.
The Fifth Amendment right against self-incrimination does not attach until the initiation of formal adversarial proceedings. You do that, you will get a one-way ticket to join Scooter. You cannot assert the Fifth Amendment if the FBI just wants to talk to you, or if the Grand Jury desires your testimony. The Grand Jury is entitled to every man's testimony.