Re: Possible answer
I read somewhere recently that as to military action, traditionally, the Marines belong to the President and the Army belongs to congress. I guess they share the Navy. :) Going all the way back to the shores of Tripoli the president has used the Marines more or less at will and that may fall short of war.
Hence, any expedition that requires the full force of the military requires a congressional act. There was a huge amount of noise about this during the Korean "conflict".
It seems it only becomes okay to call it a war after it is over.