Foiled attempts are a hard thing to prove. Anne McCaffrey had fun with them in her books -- psychics would prevent terrorist attacks by warning about them ahead of time, but then, because the attacks would be foiled and not take place, people eventually started doubting the psychics and saying, in effect, "prove it." How can you prove it? By writing it down in an envelope and then having it opened after the attack takes place? Only if you've got a total disregard for the people killed in the attack. Same thing with Bush -- they're saying, "sure, sure, you've foiled attacks -- you're just saying that to back your spying up. Prove it -- what have you foiled?" But if he did the envelope trick, he'd be in more trouble (and justifiably) for having the knowledge and doing nothing about it.
Sucks to be president. Glad I'm not!