Hell, ISIS were born from the Iraqi insurgency, which was only as successful as it was because of the poor decisions made after the invasion.
No contest. Its Bush's fault, but Bush nearly had it fixed. Things were going quite well in Iraq when he left office. Obama should NOT have agreed to remove the troops, have not consented to turn the security operation over to the Iraqi government. He should not have done Libya and we should not have backed the rebellion in Syria, we should be treating the ISIS government in Egypt as a the coup it is/was.
Those are the reasons ISIS is what it is. Those are all Obama/Hillary decisions. The outcomes were all highly predictably too, for anyone who was paying attention to the immediate after math of the Iraqi invasion. Obama and most of the people who seem so proud of their opposition than and now were to busy rubbing everyone else's face in it to learn anything. If they had the draw down would have been delayed. You can see this attitude still reflected in the media bias. Libya is a failed state now, and ISIS is there. Yet you hardly hear about anything buy Iraq. Face you and a whole bunch of others are trying to give Obama a free pass, but the fact is he made LOTS of AVOIDABLE mistakes, the SAME MISTAKES Bush made. When you have the benefit of seeing what the guy right before you got and do the exact same things, that's deeply pathetic.
The sensible alternative is just let ISIS have its day. Don't go back to Iraq, don't fight them in Syria or Libya. ISIS can't govern its not like the Taliban in Afghanistan was. The Iraqi, Syrian, and Libyan people know what a modern society looks like, they won't stand for ISIS style brutality for long. At worst it will be a perpetual series of unending uprisings and tribal conflicts. It will keep them to damn busy to attack us or Western Europe, Iran and Egypt are almost certain to be drawn in as well. We will get to find out how effective the Iranian army really still is. The nuclear issue will go away because Iran will devoting all its resources into boarder security.
The ONLY choices are go big or go home. Either we need a large enough occupying force and enough direct influence of the the decision makers in places like Iraq, Afghanistan, Syria, Libya, Yemen, and possibly Egypt or we should get the hell out! To do otherwise is going to result in spending a steady stream of treasure and American lives that only keeps things to a slow simmer over there with plenty of lawless territories for terror cells to workout how to blow up Western shopping malls and magazines. It will never end.