It's not uncommon for civil war/ insurgency to break out in a recently defeated and occupied country. It would appear the Sadr-ists and Sadaamists are launching that now. We should be able to prevail considering we were able to overcome the previous Iraq armed forces. But the conflict will be fierce and bloody. It may require additional troops to truly defeat these areas, which were not sufficiently subdued in the initial warfare. The support of the majority Shiites and Kurds will be essential.
This is the real world that a great power has to operate in to survive. There will be significant losses on both sides. May God protect our soldiers and give America the strength and wisdom to prevail.