There isn't any congressional authorization, much less a declaration of war. Is there even a good reason for the United States to be involved?
There is no better time to ask this question than now, as much of the world (me included) is disgusted by the Islamic State's beheadings of two kidnapped Japanese nationals, the second one an acclaimed journalist and humanist who lost his life trying to rescue the first.
It is easy to forget that for Americans, going to war was until recently an act undertaken only after every other alternative had been thoroughly explored and completely exhausted, that the bar for casus belli was high, and that war wasn't the standard response to outrage or international crisis, but quite unusual, a deviation from the normal order of business.