Who sent Wilson? His wife? His wife's boss who resigned after the story broke? Not only "who?", but "why?"
What was the purpose of Wilson's mission to begin with? And was the purpose accomplished?
Presuming, of course, that the original purpose was not to undermine the President...
Well, I'm guessing the ultimate who is this guy;
But as for the person immediately responsible, unless Wilson changes his story that he doesn't know who sent him, we will never get proof. However, I still think Plame persuaded her superior. It makes sense seeing as this was his baliwick anyway.
And we all know the reason why...