Bush stated his goal clearly: Regime change.
If the WMD issue proves to be fabricated in whole cloth then yes, Bush will have big problems with that.
If it turns out that there was reasonable evidence and that they were just wrong, the problems will be of a much smaller nature.
My guess right now is that the axis of weasels succeeded in buying enough time for Iraq to hide much evidence and to make the search very tough.
Secret stuff of the German nazis was discovered for years after WWII was over.
The absence of positive findings at this early juncture is not evidence of failure or fraud, yet.
Ed