His resignation letter is posted at the Smoking Gun.

(Via the Llama Butchers)

And read his detailed praise for the Bush Administration's anti-terror efforts at this briefing in August of 2002. Clarke doesn't just offer vague accolades; he actually details that striking policy changes were made quite early in Bush's term:

Clarke: So, point five, that process which was initiated in the first week in February, uh, decided in principle, uh in the spring to add to the existing Clinton strategy and to increase CIA resources, for example, for covert action, five-fold, to go after Al Qaeda.
...
Over the course of the summer — last point — they developed implementation details, the principals met at the end of the summer, approved them in their first meeting, changed the strategy by authorizing the increase in funding five-fold, changing the policy on Pakistan, changing the policy on Uzbekistan, changing the policy on the Northern Alliance assistance.

And then changed the strategy from one of rollback with Al Qaeda over the course of five years, which it had been, to a new strategy that called for the rapid elimination of Al Qaeda. That is in fact the timeline. (Emphasis added)

Realistically, how much credibility does this man have left?