Scott Lemieux comments on this article,
The apparent defection of Sadr's militias illustrates the fundamental problem: the lack of a legitimate state with sufficient coercive capacity. Iraq still doesn't have one, becuase the temporary security improvements of the surge haven't led to substantial political progress. The U.S. military simply can't create an effective state out of thin air. And this is reflected by the assertions of "U.S. officials" that we'll need to give it some more Freidmans.* Given the strategic objectives, "successes" that require the indefinite presence of high levels of U.S. troops to sustain aren't "successes" at all.A lot of the measures used to estimate "success" or "failure" of the Iraq War, such as troop casualties, civilian casualties, the frequency of bombings, or levels of sectarian violence, are very poor measures, as those numbers can change very quickly. Genuine political progress is necessary to achieving long-term stability.
Unfortunately, it appears that no such progress is forthcoming. To put it mildly, seeing Sadr's Shiite militias jockeying for power with the government does not reassure me that the Shiite-dominated government can "reconcile" with Sunni and Kurdish factions. Even assuming it wants to. Or that the minority factions truly want to reconcile with a central government.
A significant troop presence can help keep the lid on a pressure cooker but, absent political progress, sooner or later "That thing is gonna blow."
* A "Friedman", "Friedman Unit", or (most cheekily) a "F.U.", is a period of six months, referencing Times columnist Thomas Friedman's willingness to describe "the next six months" in Iraq as the period of time crucial to determining the viability of our goals, while disregarding actual outcomes.