Unable to defeat Sadr on the streets of Basra, Baghdad or anywhere else apparently, Maliki and presumably his American interlocutors are seeking to "neuter" the Sadrist movement by forcing Sadr to "disarm" in the face of control of the Iraqi Security forces by Maliki's Dawa Party and the Badr Force militiamen. Presumably, they think that a disarmed Mahdi Army/Sadrist movement would be unable to resist whatever result might be created in the elections.
Why would the Maliki/Hakim/US forces want that? Application of Occam's Razor to this issue yields the solution that those forces fear that Sadr would become stronger in the elections if allowed to contest them on an "even playing field."
Sadr's response has been to ask for the guidance of the senior ayatollahs in Najaf and Qom as to whether or not he should disarm. (Irony Alert - one would hope that he will also seek the guidance of the Mahdi in this matter) This appeal to Najaf and Qom is a strong move. He can hardly lose in this. If he is advised by the ijma' (consensus) of the hawza to retain his forces, then he will do so with religious sanction. If advised to disarm, then Maliki will be in the position of either allowing Sadr to run his candidates relatively unmolested or of being seen to have "rigged" the election against the consensus of the hawza.
Sadr is now in Qom seeking to sharpen his religious and political credentials. The Iranians' fine, complex, Florentine hand is in this somewhere. pl