A better way to deal with ISIS
So after that, I expect I would be asked, I have been asked, what would I do instead?
The first thing is to realize that ISIS grew out of disaffected Sunnis in western Iraq who felt first abandoned and then betrayed by the Shiite-dominated government in Baghdad. Unless you bear that in mind, nothing will make sense.
So with that in mind, what's the better approach? First, realize that bombing ISIS only makes them look like victims in the eyes of too many of their potential supporters, particularly those Sunnis of western Iraq. So stop it.
Next, go after the money supply. Hit ISIS economically. ISIS has been largely self-funded so far, largely by just taking what it wants, but that can't continue and is already changing. Having oil means nothing if you can't see it.
The more ISIS tries to present itself as, tries to behave as, a caliphate, as an actual government, the more entangled it becomes in a broader economy and so the more vulnerable it becomes to economic pressure.
Third, crack down on the weapons supply, not only by cooperation with regional governments but by ending the flow of US arms to the region.
Fourth, and this is perhaps the most important point, address the political grievances of local populations, particularly the Sunnis. Tell Iraqi Prime Minister Haider al-Abadi that all future US assistance to Iraq in all forms is dependent on a true rapprochement with the Sunnis and mean it.
Finally, provide humanitarian assistance to all who need it, regardless of political affiliation.
That's how you deal with groups and movements like ISIS: Don't try to beat them into submission; that rarely works and when it does it's usually just temporary as long as the underlying causes, the driving forces, remain unchanged.
Instead, you try to simultaneously deny resources to the movement while striving to remove the causes of the violence and so let the movement wither and die for lack of reason to exist.