The whole of Iraq will need to be guarded until Iraqi police forces can do it themselves. No matter if the US leaves and UN forces take over, the bombings, murders and retributions will continue for decades.
Sort of like the Palestinian conflict.

Remember, terror is the tactic of the powerless.
And there is no shortge of weapons to that hotbed in the desert.
The weapons dealers will be in there for the next few decades, making a buck. We won't even be able to protect it's borders.

Do you really think we would have given our president the permission to try and create a free Iraq all by himself, using the best of our army AND foot the bill for him?

That's what's happened....an experiment gone wrong.
But nobody will admit it.
The White House and the media spin it into some delectable morsel that you just eat up....willingly and with glee.