George Packer has written a truly enlightening and intriguing book about our descent into Iraq. Packer is a lucid and engaging writer who can clearly summarize the intellectual debate between the neoconservatives and the realists. It's also a sad book. Learning how policy is arrived out and then justified and implemented can be very discouraging.
The neocons and Bush had decided to go after Iraq for a variety of reasons before 9/11. The concern then became how to sell that decision. Shortly after the fall of Baghdad Paul Wolfowitz fold an interviewer: "The truth is that for reasons that have a lot to do with the U.S, government bureaucracy, we settled on the one issue that everyone could agree on, which was weapons of mass destruction." The real rationale for the war was to realign American power in the Middle East, toward a democratic society and away from Saudi Arabia, home of the Wahhabi sect that virtually controlled Saudi society and government and had been the home to almost all of the 9/11 terrorists. (See Sandra MacKey's very excellent book on Saudi Arabia -- The Saudis -- for a detailed view of what it's like to live in such a theocracy.)
The job then became to selectively use pieces of intelligence that supported their common justification. "Just a year earlier, Iraq had been viewed as an outlaw state that was beginning to slip free of international constraints and might present a threat to the region or, more remotely, the United States in five years or so. Now, suddenly, there wasn't a day to be lost. . . It didn't matter that there was no strong evidence to back up the doomsday prognosis."