Spencer Ackerman has another excellent post on the political and military problems the US and the Shi'ia face going forward, now that the Sunnis have exploded. I hadn't been reading him lately, shame on me. He's quite good. Here's the bundle that together create the big problem the miiltary faces (he doen's even bother to explicitly refer to the lack of trained and loyal Iraqi security forces and police, since that's such a fundamental given):

First, while the U.S. had months to prepare the invasion of Falluja, the inflammation of other cities, including once-a-model-of-success Mosul, appears to have caught the U.S. military somewhat off guard and will subsequently prompt a more ad hoc tactical strategy to reclaim those cities, if such operations occur. [as I argued in other comment, I agree re shift to a more ad hoc strategy required, but not that the fact of a counter-offensive wasn't anticipated, ed. Second, it's unclear whether the 140,000 U.S. troops can sustain an operations tempo comparable to what seizing Falluja required. [not just unclear, they can't, ed.] Third, reconstructing Falluja is a massive undertaking of a sort that the U.S. has proven unable to handle over 20 months of occupation, and to expand those needs around the country at this late hour represents a serious strain on resources. [at this late hour? we've only just begun. Actually, the bigger problem pointed to by Ackerman in his piece today is that it's going to take an immense effort to hold Fallujah, let alone reconstruct it ed.] And finally, the elections themselves are extremely likely to represent a new level of Sunni disaffection with a now-formally Shia government, which risks replenishing the ranks of the insurgency.