You seem to forget the logistics of the situation in early 2003. The military buildup in the Middle East either had to go into Iraq, or go home, by the spring of 2003. As it is, they launched the war pretty much at the last possible moment where they could defeat the Iraqis before the summer heat made major unit combat impossible (ever sit in a tank baking under the MidEast sun with 130F in the shade?). If Bush had waited only a week or so more, his military advisors would have recommended scrapping the invasion at least until the end of 2003, when it got cool again.
But that would mean keeping the troops in place for 8-9 months before a new invasion window opened:
- Diplomatically, keeping so many troops in the MidEast for that long would already be very difficult, if not impossible.
- Operationally, the forces would be forced to hunker down and take the heat as well as they could, far away from their normal training facitities, which means that if they did have to invade 9 months later, they would be out of practice due to substandard training, and U.S. casualties would be far greater. Their equipment would also not be in the best of shape, hot having the maintainance facilites they have back home.
- Economically, keeping the forces in-theater for an extra year would be extremely expensive - the better part of $100 billion, as I recall. The public and Congress would never accept that cost, especially if there is no knowledge of whether they would be needed in the end. Getting the troops deployed there cost a huge amount of money, and getting them home again would have also cost a bundle. Congress would also never approve a redeployment again in the spring of 2004, should Saddam decide to stall again.
- Strategically, with the knowledge that for 9 months, a huge chunk of the U.S. military would be rendered practically useless, unavailable to be redeployed elsewhere, and rapidly losing combat efficiency due to lack of proper training facilities, Congress and the U.S. public would find keeping the troops in-theater for that long unacceptable.
- Politically, pulling back the troops without using them and without having resolved the WMD issue would have been a major, major political defeat for Bush, Blair and all the coallition members, from which they would probably never recover. They certainly would not have had the prestige and influence to repeat the deployment in 2004.
We know from interviews with Saddam's officials that Saddam was hoping to force the U.S. to delay an invasion until it was too late - another week or two would have been enough. Once it was clear that an invasion was no longer possible, he would have started obstructing the inspections again, knowing that there was nothing the U.S. could do about it any more. Remember his goal - he wanted to leave the seeds of doubt about his WMDs so that other MidEastern countries would fear him.
Therefore, If the invasion had not started when it did, Saddam would still be in power, the U.S. would have suffered a major diplomatic defeat, there would still be questions and doubts about WMDs, investigators would go home with inconclusive evidence, and the Russians and France would have probably succeeded in removing the sanctions (through a General Assembly vote), thus freeing up Saddam to re-arm - this time for real.
Honestly speaking, even with 20/20 hindsight, the decision to go to war was the correct one - even Kerry has agreed with that.