His mistake:
If one of my mistakes was to trust men like August Hanning, another larger mistake was to put my trust in the Bush administration, not so much on matters of intelligence—faulty intelligence was a near-universal phenomenon—but on matters of basic competence. I will admit to a prejudice here: I believed—note the tense, please—that Republicans were by nature ruthless, unsentimental, efficient, and, most of all, preoccupied with winning. It simply never occurred to me that Donald Rumsfeld and Dick Cheney would allow themselves to lose a war. Which is what they have very nearly done.[…]
What the world is confronting five years after the invasion—the mess that Gen. David Petraeus is attempting to clean up today—was almost entirely preventable. It’s not only my encounters, inside Iraq and outside, with senior figures of the Bush administration that have convinced me of this; the investigations conducted by George Packer, Tom Ricks, Bob Woodward, and Michael Gordon, among others, have unearthed thousands—literally thousands—of mistakes made by this administration, most of which were avoidable.
The Dish 