More from Marc Lynch. After quoting a Saudi Arabian editorial suggesting that Iran has abandoned Muqtada al-Sadr now that it has more useful allies in Baghdad, he summarizes the various guesses floating around about what's really going on in Iraq right now:
So you can add the  "Iran is liquidating its no longer useful proxies" theory (which would fit this general line of speculation about Iran's doubts about Sadr and preference for the simultaneously-US backed ISCI) to the generally most prevalent (in the Iraqi and Arab, not just Western, media)  "Maliki and ISCI are liquidating their more popular rivals ahead of the provincial elections" theory; the optimistic  "Sadr has lost power and now's the time to take him out" theory (thus far not borne out by the course of the fighting, but who knows — it's early); Maliki's own  "it's time to establish state sovereignty over a 'lost' province" theory (which Bush, of course, has embraced, and is supported by the reporting that the Iraqi Army began its preparations for the attack months ago; but then why isn't he taking on the other militias and warlords? and why would he start now, and in Basra?); and Reidar Visser's  "Maliki is trying to build a power base in the Iraqi Army" theory.
All numbering added by me for handy future reference.