That's it. Moqtada al-Sadr and Grand Ayatollah al-Sistani are demanding a popular referendum on the SOFA the US is trying to impose on Iraq. By demanding a referendum the Shias are achieving three results:
a) they are completely by-passing the National Assembly
b) they are making the SOFA an election issue
c) any referendum on the SOFA will be a de-facto referendum on the US presence in Iraq
The Imperial Command is now in a loose/loose situation. If it allows the referendum to go ahead it will suffer a highly visible and embarrassing political defeat and the legitimacy of the US occupation (assuming there ever was one) will be *officially* down to zero. If it bans the referendum it will prove to the entire world that is is an occupying force which does not give a rat's ass about what the Iraqis think (we already know that, but this will prove it).
It looks like the Shias have effectively checkmated the Occupation.