The most sensible argument for the invasion was not that Hussein was about to strike the United States or anyone else with a nuclear bomb. It was that containment could not be preserved indefinitely, that Hussein was repeatedly defying the international community and that his defiance appeared to both the Clinton and Bush administrations to be gradually succeeding.
(Kagan’s argument is limited in scope, perhaps due to the size constraints of a newspaper column. I would add to his points this one: in the sewer of middle-eastern Islamist nationalism that produced terror attacks culminating in Sept. 11, the US needed to start reversing the process by making an example of one of our enemies. Afghanistan was the right place to start, since the Sept. 11 terrorists came from there, but having subdued Afghanistan we needed to make clear that we saw what we were doing as more than a police action against Al Qaeda. Saddam Hussein’s Iraq made perfect sense as our next objective, due to its combination of persistent belligerence toward us, a history of external aggression and extreme brutality, and WMD use and possession.)
(Kagan link via Martin Devon.)