Jeff Cooper is an actual law professor, and so much more qualified than I to discuss the legalities of declaring war on Iraq sans Congressional approval. He read the Security Council resolutions I referenced earlier and reports that their goals have been achieved. So there you go.
Parenthetically, and I mention this because it’s been brought up from time to time, Clinton also used the 1991 Security Council resolutions as justification for military action against Iraq. So it’s not as if Bush doesn’t have some precedent. Clinton’s stance was that enforcing the no-fly zones was a means of preventing further Iraqi aggression against neighboring states, which was in fact mandated by the UN. Although the UN didn’t approve the no-fly zones. Muddy waters.