Chris Bertram, as well as Eric Tam highlight the American Prospect article by William Galston on just war theories and Iraq. The key quote:

Saddam Hussein may well endanger the survival of his neighbors, but he poses no such risk to the United States. And he knows full well that complicity in a 9-11-style terrorist attack on the United States would justify, and swiftly evoke, a regime-ending response. During the Gulf War, we invoked this threat to deter him from using weapons of mass destruction against our troops, and there is no reason to believe that this strategy would be less effective today. Dictators have much more to lose than do stateless terrorists; that’s why deterrence directed against them has a good chance of working.
In its segue from al-Qaeda to Saddam Hussein, and from defense to preemption, the Bush administration has shifted its focus from stateless foes to state-based adversaries, and from terrorism in the precise sense to the possession of weapons of mass destruction. Each constitutes a threat. But they are not the same threat and do not warrant the same response. It serves no useful purpose to pretend that they are seamlessly connected, let alone one and the same.

While well-intentioned, I believe that this construction has a fatal flaw.
Before I get into it, let me explain that I am not today waving flags to encourage an invasion of Iraq. I am a fence-sitter, probably tipped slightly in favor of invasion but anxious about the prospect that will face us afterward.
But as to this argument, I have a serious problem. First, that any WMD attack on the US (or any of our forces protected proxies) will certainly not be readily traceable to Saddam, or anyone else with the absolute level of proof that I believe would be required before some people would grudgingly support the idea of war.
Remember that there are many who do not today believe that Al Quieda was behind 9/11, and it is unlikely that we will get access to video of Saddam handing Joe Terrorist the keys to a truck loaded with smallpox ampoules, or of Saddam pushing a big red button labeled “Blow Up Tel Aviv”. As I have discussed below, the probable response looks more like:

“Wow!! Bummer about Tel Aviv!! Who would be crazy enough to smuggle a nuke in there? Wasn’t us, promise!! No, really!!”
While the tame game theory model suggests that he and others can be managed successfully through boundary and consequence-setting, the only thing that might work would be something Godfather-like:
If anything bad happens to me; if I catch a cold and go to the hospital; if I get hit by a car while rollerblading drunk; you will die. You are now the guarantor of my wellbeing.

and I have a hard time imaging some of the more profoundly antiwar folks being willing to accept anything like this.
Let’s talk about this for a minute.
I will not pretend to be an expert on warfare, conventional or otherwise, but I have studied and practiced a number of ‘real world’ martial arts for a number of years.
And the consistent most significant problem that is shared by all of them is ‘threat identification’; i.e. how do you know who is a threat and who isn’t? It’s easy to know on the mat or at the shooting range, but much muddier out in the streets and alleys of the real world.
…actually, I just realized that this is a longer and more significant point than I originally thought, and will polish it and try and post later today. Sorry about that!