Bush was able to refer to the Iraq Liberation Act 1998 (
https://en.wikipedia.org/wiki/Iraq_Liberation_Act), passed by Congress and inked by President Clinton. The act called for US co-operation with Iraqi democratic movements rather than military action, but it was, rather obviously, a bad and stupid piece of law.
Even so, if the Americans had been prepared to commit sufficient boots on the ground to ensure Iraq's security after the overthrow of Saddam -- which would probably have required a considerable expansion of the US military -- things wouldn't have been so bad.
Instead the US was stuck with the 'Rumsfeld doctrine', which stated that 'full-spectrum dominance' (computers and stuff plus air power, even though not very much air power was committed to Operation Iraqi Freedom by comparison with Operation Desert Storm) reduced the need for boots on the ground.
In fact, of course, boots on the ground really do matter, and the US had made the same mistake before, in Normandy in 1944. They thought that armour, artillery, air power and logistics rendered the infantry all but redundant, so only the least educationally qualified men were selected for infantry and no one selected for other specialist tasks was even given basic infantry training. (Compare with the British service, where even Spitfire pilots had all learned to march and drill and use the Lee-Enfield rifle, the .38 revolver and the Bren gun in basic training, in case they failed their specialised courses and had to be remustered as infantry.) And just two weeks after D-Day, First US Army ran out of trained infantry casualty replacements and had to start combing untrained men out of the Services of Supply and the Air Corps (there were a lot of surplus radio operators) and so on, and shoving them into frontline foxholes, a hundred yards from the nearest German, with a rifle they'd never seen before, let alone fired. During the whole of the Normandy campaign, only one-third of the casualty replacements sent to the US infantry units were even rifle-trained. The effect on the US infantry casualty rate was... interesting. And tragic.