A well-presented discussion of the things the libs claim, and the evidence that prove they're wrong would work wonders. Much as I like GW, I don't think he is articulate enough to do it.
But Dick Cheney could do it.
as soon as he made the speech, anonymous CIA sources would leak conflicting information to the media - who would run the stories as fact to discredit whatever Bush was saying.
The agency must be cleaned out from the inside first, you can't send the President out there to make arguments based on US intelligence - when forces within the same agency are working the opposite side of the street.