Someone didn't read the 9/11/2001 commission report or spent time watching the debate between Clarke and the White House, in which the White House retracted their statements because of other Federal agencies backing Clarke up such as the CIA and the Federal Bureau of Investigations.
Even before this investigation, a valid reason I believe Clarke is because he was the lead expert on Counterterrorism and in 1999 investigated any possible connection with Al Qaeda and Hussein to check if Binladen might seek refuge in Iraq. By the end of 1999, Clarke concluded there was no proof of any connection between the two.
Here's a link to a few interview and criticism of him:
http://www.youtube.com/watch?v=-yRjSOyyZic
And, to be perfectly clear, most of the information indicates that Condaleezza Rice had done her job poorly.
Interestingly enough, during 2008, former CIA director George Tenet published his own book and criticized Bush's administration, mainly Rice, for their inactions during 9/11. Which provided even more collaboration to Clarke's statements.
http://www.youtube.com/watch?v=ffjXthuNn60







