As I noted in the post above, Spencer Ackerman " doesn't even bother to explicitly refer to the lack of trained and loyal Iraqi security forces and police, since that's such a fundamental given." John Robb at Global Guerillas sees the weakness not just as a given, but a very much worse given that it even was before this month. An irremedial given as far as I can tell. He views the lead-up to Fallujah and the fighting there as the final melt-down of the Iraqi security system. Definitely worth a read. Bottom line:

The systemic failure of Iraqi security, creates the following situation: * Ethinic passions on the rise. The use of Kurdish fighters in both Fallujah and Mosul has exacerbated the insurgency. * The US in the hot seat. Left with the security burden, the US is in a tough position. Its firepower intensive tactics (force protection 2GW methods) are causing more damage to the Iraqi government's legitimacy than it provides. Further, we also don't have the troops in country to even approximate what is needed to provide a modicum of basic security. * Complete system failure. This has set the stage for ongoing attacks by innovative guerrilla entrepreneurs on all other aspects of globalization in Iraq (people, resources, and investment). The economy will remain in failure, as will the state.

But in the Murphy's Law world of Iraq, it's pretty clear that "complete system failure" isn't as bad as it's going to get.