US troops may be moved from Anbar to Baghdad, and replaced in Anbar by Iraqi forces.
By moving Iraqi forces in to Anbar, we do one of two things, either of which is to our benefit.
1. Either the militia infiltrators desert rather than serve in Anbar or
2. They stay and fight, and thus attrit themselves clearing up the terrorists in Anbar.
In either case, they are far less capable of keeping up sectarian violence in Baghdad, especially as there will be far more US forces there to stamp hard on any attempt by renegade security forces to stir up trouble. With militia infiltrators or without (a lot of the militia types seem to be wanting some payback - taking out their pound of flesh from the Sunni who oppressed them for so long; Anbar is the place you want to be, if you want to pay back your Sunni oppressors - so, some of the milita infiltrators may very well stay in when transferred to Anbar), the Iraqi forces sent to Anbar - backed by US power - will likely prove more than a match for the terrorist forces in Anbar.