By "declaring war," I think he means that we should declare war against Islam. Just a guess, mind you.
That would be a little general and excessive. Sort of like declaring war on all Buddists, when the problem was the government of Nippon. We could start with a fairly short list of Islamist groups, adding language that would prevent a mere name change from "letting them off the hook". The list could be expanded as needed, but only by a new declaration from Congress, or perhaps just by action of a special Congressional committee along with the President.