Clearly, Iraq wasn't attacked because of one man's lie. I can still vividly remember Powell making claims about the mobile weapons units - am I, um, mis-remembering him actually showing satellite images? At any rate, to state the obvious, here's one former CIA analyst:

There were people at the time who doubted what Curveball was saying, but if the administration doesn't want to believe it, it doesn't make much difference.

I know I keep on banging on about this, but these two letters from 1998 are still there: one to Clinton and one to Gingrich, both stating that the "the only way to protect the United States and its allies from the threat of weapons of mass destruction [is] to put in place policies that would lead to the removal of Saddam and his regime from power", and that the US should "be prepared to use.. force to protect our vital interests in the Gulf - and, if necessary, to help remove Saddam from power."

The writers' unshakeable conviction in the presence of WMD is backed up by an equally fervent belief that backing down would mean "an incalculable blow to American leadership and credibility."

A fun game: match the letter signatories to Bush administration positions. One of them is even in the Grauniad article above, saying:

It's the job of intelligence agencies to distinguish between defectors who claim to have something to say and defectors who are lying and they obviously didn't do their job. The Germans didn't, and we didn't.

Well, actually, intelligence agencies have a dual purpose: to sort fact from fiction, and to help create a version of the facts that fits their state's foreign policy. I've never really been sure how the two are meant to co-exist.