From BBC:
Mr Sadr's bloc, which has six cabinet ministers, is trying to press Prime Minister Nouri Maliki to set a timetable for a US troop withdrawal.A couple of things come to mind as possibilities:
Mr Maliki has refused, saying a pullout depends on conditions on the ground.
Analysts say Mr Sadr holds great power among Iraq's Shia majority, but the unity government is likely to survive.
Last week, tens of thousands of people attended a rally in the Shia city of Najaf organised by Mr Sadr to protest against the continued presence of US-led troops in Iraq.
Mr Sadr did not appear at the rally in person. US officials say he has fled to Iran, but aides say he is still in Iraq.
- al-Sadr believes his power is sufficient to challenge the Iraqi government and the U.S. and is severing political ties in preparation of escalated violence with the support of Iran and Syria... or
- al-Sadr believes the U.S. is ready to escalate its efforts to weed him out and is desperately trying to rally the population and his troops to fend off attacks against him until U.S. public's patience runs out and Democrats can pull off a withdrawal at any cost