But it's not a Declaration of War. If it is over quickly, then it works. But if it goes on through an election cycle some will take advantage. They could have had a Declaration of War. Mistake not to.
congress would not have given a declaration of war in 2001.
The only problem is, who do you declare war to? Declarations of war by definition are between Nation states, not amorphous groups. That, and formally declaring war tends to show a level of commitment that no government since WWII has been able to get.