I've read a number of reports indicating that we gave arms to the Syrian rebels, many of which are part of ISIS/ISIL now. We had a lot to do with what is happening in Syria.
Which leads us back to the point:
What do we do?
We could stand back and do nothing. Then the area becomes a safe haven to plan attacks on us.
We could arm the locals (who IMO would just be using us while we are an enemy of their enemy). When they are done with us we run the risk of them turning the weapons we supplied on friendlies and even us.
We could draw a REAL line in the sand. Then we end up guarding an area for decades. (see Korea)
We could spend money getting intelligence from bad characters or spies, then send in assassins/drones when we get a chance. Then we get bad information and hit innocents, women and children they are hiding behind.
We could go in full force and clean things up again. Then we get another unpopular long and expensive buildup where our country runs out of patience again.
None of these are great options. Either way we get blamed for causing it, or not doing enough given our resources. I personally don't blame Bush for trying the last one given the equally bad track record with the others. IMO Obama doesn't seem to have the stomach for any of them, and seems to try the most politically expedient one.