Well like I said a couple of posts ago. He hinged the whole thing on WMD's. Not too bright. There are a whole list of reasons he could have listed but he chose WMD's. He could have listed the UN Violations, expulsion of UN inspectors, etc. But Bush chose WMD's alone and that was not to smart. Look how it bit him in the butt. You may/would not agree to these reasons (if he gave) them but at least he wouldn't have had it haunt him as the sole reason for invasion.
He didn't chose UN violations because it would need a UN vote, and everyone at the UN knew Powell and his team were making stuff up to create a war.