Since ISIS/ISIL claims to be a state would not a declaration of war by Congress be appropriate and let Barky deal with that reality? I would consider the blatant murder of an American citizen, coupled with ISIS rhetoric to be a legitimate causus belli. This would no longer be the war on nouns with which opponents derided the war on terror, but a legitimate war against a state with reasonably defined territory and an announced capital city.
Unless the objective is going to be exterminate all ISIS members. Then I won’t support it.