A foriegn organization effectively drove several cruise missles into U.S. Targets, killing thousands. How can you not call that an act of war?
A foreign military has been waging a low level conflict with us for the last few years. This is know as a campaign. This campaign is not defined by the rules of the 1940's, but it is a campaign none the less. The military may not be associated with a "State" but that does not make it any less of a threat.
We are at war. Our response must be viewed in the context of war.