I am not so sure that there was a failure at all here. I am certain that the Bush administration did not lie to us or exaggerate their claims of danger. If anything, they understated the danger (probably being politically careful). We know that in the past, Iraq had large stockpiles of various weapons because they admitted it. They then claimed to have destroyed it all but could never convince anybody that they were telling the truth. Our intelligence services reported various facts (most of which are not public), but I have not seen any of them refuted yet. They also presented many partial pictures of what was going on in Iraq and the Bush administration chose to act on a conglomeration of past facts, current facts, and possible future scenarios that included unacceptable levels of risk.
This is not failure, it is making decisions that have to be made with incomplete data and making them in the best possible manner within the limitations. These limitations were known at the time, and any guesses on filling the unknown data were just that - guesses. We did not know how far along his weapons programs were and we did not know what had happened to all his weapons stockpiles, but that lack of knowing, and Iraq's determination to keep us in the dark was threat enough to act.
David Kay said today that while the corruption in Iraq may have disguised how active the weapons programs actually were, that same corruption made Iraq an even MORE DANGEROUS place than was previously thought, because it was nearly inevitable that in such an environment, a terrorist buyer would connect with an Iraqi seller.