Simon: That is a critique of Obama that I can agree with.
It is kind of difficult. After 9/11 Afghanistan had to go, but then Iraq also got invaded. I happen to think that a very good case could be made for invading Iraq in 2003 (not involving WMDs), but the instability showed just how unpredictable the removal of a cruel regime could be.
Then came the Arab Spring, Libya collapses, Syria is not looking good and using WMDs in the battlefield and what do you do?
Looking at what happened, harsher action against ISIS early on would IMO have been a good idea (though ISIS was still fairly fringe at the beginning of the conflict), but from what I can read Pentagon did not have a clear idea about what would happen if you supported some given faction in the conflict (rebels or Assad).