From what I've read, Bush had enough people telling him about possible chemical and biological weapons that one could give him the benefit of the doubt and say no lie there. But, those types of WMDs couldn't by themselves tip the balance in favor of war. For that, nukes were needed. There was even less certainty about Saddam's nuclear activities. Bush needed one shred of evidence to convince the public, because the aluminum tubes, by themselves weren't pursuasive. Hence, the manufactured document about the Yellow Cake uranium. There is your lie. The lashing out at Wilson was further evidence. That was the fatal mistake.
The problem with Bush's style of take-no-prisoners politics is that when you play that way, people just are not predisposed to give you the benefit of the doubt when you screw up.