I seem to remember that when we withdrew we said we’d be right next door if you need us...
Obama could send in the marines any time if he wanted to. I think that what is happening is what is supposed to happen; they war-gamed it and it is proceeding according to plan.
The Al Qaeda rebels of ISIS in Iraq, are allied with (if not the same) Jihadists in Syria that Obama was arming and supplying and equipping to overthrow Assad.
Obama is helping to assist the Jihadists to create a global caliphate.
Obama supports the Sunni brand of Jihadist Islam - so it should be interesting to see what he does (if anything at all) once Iran decides to get involved.