... the strategic problem for ISIS has become much simpler.
First the British and the Germans and now the French have backed out of airstrikes in Syria against ISIS. All have sizable Muslim populations and the French ones can be quite restive. See also: cars, burning of. The risks of rioting in their cities outweighed the nebulous benefits of a dilatory bombing campaign. We are effectively isolated in this effort with no allies of any consequence at our side.
For ISIS, the problem has been reduced to getting the US out of the way. They can wait us out, a strategy that has born fruit everywhere or they can take more direct action. Would we still have the stomach for the fight once chunks of the US electrical grid have been knocked out with some well-placed acts of terror?
More to the point, would we be willing to spend the men and money required to go after them in force over in the Middle East with no large allies?