I think he imagined that the US military is better than it actually is. This has shown that it isn't. I think if anything it will have shown other rogue states that DO have an intact military that the US is not the massive power it imagines itself to be.
You have GOT to be kidding! That's actually one of the big headaches the President had, that the US Army ran over the Iraqi army too fast. What took months and weeks a decade ago, now took a matter of days. Even if you want to look at it from a "cold, numbers" point of view, loosing 500 people over a one year period in a war is probably acceptable. What people forget is that the US army is occupying a country of some 40 million people. Hell, last year a 1,000 people were murdered in the city of Chicago. A city with a population of only 3 million.
One thing I will agree with is that the US army is not designed to occupy and police a country. This, to me, was Bush's biggest mistake. He had two options. One, cut loose the dogs of war, take out Saddam and his army and then leave or two, take out Saddam and his army then turn over the reconstructing process to the UN.
This "nation rebuilding" process is going to be tough. But he's got us in there now and if he cuts loose the people of Iraq before the job is done (like his daddy did) they'll be hell to pay.