The AUMF was only a 'kind-of' declaration of war; given the attention span of Congress, it must surely be past its sell-by date by now. But even in war, the president isn't the King of America.
Uhh, let us see, how about, just to pick one, George Bush.
Actually, the AUMF authorized resumption of the 1991 Gulf war -- which had been on hold during a cease-fire that was contingent upon Saddam's full cooperation with UN resolutions.
Need I mention that Saddam was anything but compliant?