... but I just can't see Powell in this role.  

IMHO, he's a man with wounded integrity who was ill-used by the assbags in power.  He lied for them before the UN and the world, for which I'm sure he feels very, very sullied (as well he should).  That, at least, had a quasi-defensible motive (in Powell's mind): to bring down an awful tyrant whom he'd opposed for over a decade.

But this, an unmistakable case of political vengeance, this seems beyond the pale for Powell.  There was no other way to interpret it or parse it or rationalize it.  No one could possibly delude themselves into thinking the Plame leak was anything less than public punishment and intimidation.

I really don't want to think Powell would knowingly sink that far.

It would account for Powell going before the U.N. and putting on his freak show. A move on his part to cover up the guilt for leaking about the leak. He was pissed about the outing of Valerie P. and he outed the leaker, but then the good soldier felt guilty for betraying his leader. So what does he do, puts himself out there in front of the entire world making the case for war.