A reader writes:
There may be no rational explanation.
A shrewd operator like Cheney might well have foreseen that outing Plame would produce a storm of inquiries and bring more, not less, attention to the dubious WMD argument for war. But he went ahead anyway. Possibly he was sending a signal to any restive CIA analysts to keep their mouths shut if they wanted to keep their jobs. And given an acquiescent Congress and easy-going media, he may have thought there would be no consequences.
But I often get the impression that Cheney is just barely keeping a lid on his anger and spite. Maybe this time it blew. The visceral need for payback trumped calculation.
Then again, maybe he isn't as shrewd as we all assume.