BeardedBruce:

Krauthammer's point is that if the person committing the crime is not charged, then the lack of recall under questioning "was no big deal and shouldn't have been prosecuted in the first place"

To quote Arne,
"The perjury statute (18 USC § 1621) requires that the lie be about a material fact. Not just about something embarrassing "

If the crime was not prosecutable, how could a lie be material?

There was a criminal investigation (specifically, as requested by the CIA, of -- amongst other things -- a violation of the Intelligence Identities Protection Act), and as Fitzgeral explained on more than one occasion, Libby's lies had the effect of hindering that investigation and possibly preventing any prosecution of such violations (by Libby or by others).

Let's deal with this foofrah about Armitage here once and for all: It doesn't matter if Armintage (legally or illegally under the IIPA) disclosed the classified information to Novak first or later. That someone else has also committed a murder will not excuse you for yours. And if there was a conspiracy to get this information out to the public in an attempt to discredit Wilson (or punish him, or whatever stoopid rationale they had for it), that would also be a crime.

Libby's obstruction prevented a full investigation of the corcumstances of the outing, and that is a crime.

Cheers,