The White House says it is fighting ISIS, but its Iranian and Iranian-backed partners say the war is about killing Sunnis. "There are no patriots, no real religious people in Fallujah," said the leader of one Iranian-backed Shiite militia. "It's our chance to clear Iraq by eradicating the cancer of Fallujah." That doesn't sound like the kind of ally the United States should be embracing. That sounds like the United States taking sides in a sectarian war, against the Sunni Arab regional majority.
There is no way to defeat ISIS unless the administration can get Sunni Arab leaders, especially tribal sheikhs, to join the fight. Only they have the local forces and knowledge to root out ISIS. But obviously no tribal leaders will enjoin their brothers to open up a Sunni civil war so that the Shiites and Iranians may profit from them spilling each other's blood.
To destroy ISIS, the United States will have to move against the Shiite groups that are terrorizing Sunnis. That's precisely how the surge worked. But that hasn't happened with this White House for the same reason that the administration never moved to topple Syrian despot Bashar al-Assad—Obama doesn't want to get their Iranian patrons mad.