Can the US attack Iraq without UN approval?
Absolutely. While there are political and diplomatic benefits to getting UN approval, it’s certainly not necessary. President Bush didn’t get permission to invade Afghanistan, President Clinton didn’t get permission to bomb Kosovo, President Reagan didn’t ask about invading Grenada, etc, etc. This isn’t just an American thing either. France hasn’t asked for permission to fight with rebels on the Ivory Coast, China didn’t ask for permission to swallow Tibet, Russia didn’t ask permission to blast Chechnya, and on and on it goes. Nations regularly ignore the opinion of the UN when they find it inconvenient and we will do so as well if it comes to that.