When you think your guy is going to be accused of something accuse your opposition of it first. In this case it is Plame being accused of lying under oath. The Republicans know that Toensing is going to be accused of lying under oath, because she did. They need to blunt the accusation so they accuse her opposition, Plame, of doing it first. I will think of other examples of this.
I noticed it about four years ago. On some news magazine show a Bush surrogate would come out of nowhere with some accusation that seemed out of left field. Within a week their administration would be caught doing exactly what the they had accused someone of the week before. I thought, this is brilliant. You put your opposition in the untenable position of saying essentially "well, they did it too." Here in the Plame case we get to witness it first hand.