Obama did not fight for or care if the U.S. got a SOFA agreement with Maliki, and minus a high level presidential push for one the U.S. did not get it.
With that and with the U.S. not even giving all the aid and assistance it had agreed to give without a SOFA, U.S. leverage with the Iraqi government amounted to nil, and the Iraqi leader, Maliki, began governing more as a Shia Muslim leader than the leader of Iraq.
As the Sunni anger with Maliki’s Shia-centric governance grew, so grew the numbers of outraged young Iraqi Sunni men who began to see ISIS as preferable to Maliki.
Two bumbling idiots, Obama and Maliki, helped produce the soil in Iraq for ISIS to grow in.
And since Iraq has no real borders now, I would expect Iran would be plotting to take over Shia dominated Baghdad.
The Shia have been increasing in Baghdad the last 30 or so years and I believe now they are the dominant population of Baghdad.
The Sunnis could flee Baghdad and join with ISIS. -Tom