Following the "troop surge" of January 2007, the rate of insurgent attacks in Iraq was low and trending lower.
If the level of U.S. security assistance had been modulated by facts on the ground, Iraq's democratic institutions would have continued to take root and there would have been no ISIS.
When you are operating a brand new nuclear reactor, you don't say "our simulator says we should be able to pull the control rods all the way out, and there won't be a meltdown, so let's pull the control rods all the way out." No, you very cautiously pull the control rods out, a millimeter at a time, to verify that the system reacts as the simulator predicts.
Iraq should have been handled just as cautiously. Instead, the control rods were abruptly pulled all the way out, and we got the meltdown of ISIS.
The Bush Administration's "Status of Forces Agreement" is not an excuse for cutting and running. Imagine Japanese officials in 1947 saying "we don't want to extend the Status of Forces Agreement, therefore the U.S. occupation must end." Douglas MacArthur would have laughed his ass off!