You have to check out this Slate article from March 31:
http://slate.msn.com/id/2098067/Here are some snippets:
In the short story "Silver Blaze," Sherlock Holmes solves the mystery of a stolen racehorse by observing that the stable's guard dog didn't bark—hence, the intruder was not a stranger.
The mystery of whether Richard Clarke is telling the truth about President Bush's counterterrorism policies might be solved the same way: Which dogs aren't barking? Amid all the administration officials bombarding the airwaves with denunciations, who has stayed mum?
The answer: Secretary of State Colin Powell and CIA Director George Tenet, and their silence speaks loudly.
If Clarke is spewing nonsense—if the president and his national security adviser really did consider al-Qaida an urgent matter—Tenet is the man to say so. It's hard to imagine that the White House hasn't tried to recruit him to do so. Yet so far he hasn't.
Tenet is not the only quiet dog. One of the hounds that the White House did unleash—Secretary of State Powell—not only declined to growl, but practically purred like a kitten. Interviewed on Jim Lehrer's NewsHour, Powell said: "I know Mr. Clarke. I have known him for many, many years. He's a very smart guy. He served his nation very, very well. He's an expert in these matters." His book "is not the complete story," but, Powell added, "I'm not attributing any bad motives to it."
Asked if he had been recruited to join the campaign against Clarke, Powell replied, "I'm not aware of any campaign against Mr. Clarke, and I am not a member."