Conflict Between Shiites in Iraq?

Recently advocates for staying in Iraq have argued that we can use our leverage as a "power broker" to compel the Shiites to accept a government that includes the Sunnis. The Bush administration appears to be listening, as the Bush administration has not denied pressuring Iraq's Prime Minister al-Jaafari to step aside. In doing so however, I'm not sure that this is what they intended:

Iraq's dominant Shiite political bloc fractured Sunday when its most powerful faction publicly demanded that the incumbent Shiite prime minister resign over his inability to form a unified government.

The developments suggested that a new phase in Iraq's convulsions might have started by opening a possibly violent battle for the country's top job between rival Shiite factions, which both have militias backing them. The incumbent prime minister, Ibrahim al-Jaafari, has said he will fight to keep his job, and his principal supporter is Moktada al-Sadr, a rebellious cleric whose Mahdi Army militia has resorted to violence many times to enforce his wishes.

Al-Jaafari's days are clearly numbered. He is apparently in the pocket of Sadr and his more violent militia, which is suspected of being responsible for many of the killings of Sunnis being carried out primarily in Baghdad. As such it is intolerable that he remain the Prime Minister, and apparently a significant portion of Iraqi clerics agree that he must step aside. Whether they have done so because we have requested it is unclear, though it's hard to think otherwise.

Whatever al-Jaafari threatens, Sadr must know that he cannot win a fight against other Shiites supported by Ayatollah Sistani. He would be seriously over-playing his hand to believe so. What can hope is that once Jaafari steps down-as it appears he has no choice but to do-progress towards forming a new government can again be made.