Many elements of different Shia groups have infiltrated the military, police, and government. This is why the Shia death squads are mostly comprised of the police themselves. The Bush administration doesn't want to face this reality because it looks bad.

It's undeniable that once we leave, sectarian violence will escalate. But the thing is, is that it will escalate anyway. The Bush administration is probably just waiting until the next Presidency so that the blame of violence erupting in Iraq will be placed on the Democratic President who pulls the troops out, inevitably causing more American deaths just for the sake of destroying the Democratic Party. It's sick, but it highlights the ideology of the Bush administration who loath their political enemies perhaps just as much as the terrorist enemy. Either that or they're completely ignorant of the situation in Iraq, and are completely blind and retarded to think that they can stop the violence via the methods they are using and have been using throughout the entire course of the war.