They didnt keep him around for long.
I agree that Clarke's an opportunist, especially after listening to his interview on Fresh Air. Sounds like sour grapes because he wasn't bending Bush's ear regularly. However, that doesn't discount the accuracy of the things he said about both Bush and Clinton.
In the case of protecting the US from terrorism I don't think Bush has done a very good job of that. Significantly, he pursues a single-minded policy against Iraq, in spite of their lack of involvement in 9/11. What was the immediate threat to the US that Iraq posed again?