Al-Sadr and his political allies have largely disengaged from government, thus contributing to the political paralysis noted in a White House report last week. That outsider status has enhanced al-Sadr's appeal to Iraqis, who consider politics less and less relevant to their daily lives.
Al-Sadr has been working tirelessly to build support at the grass roots, opening new storefront offices across Baghdad and southern Iraq that dispense services that are not being provided by the government. In this he seems to be following the model established by Hezbollah, the radical Lebanese Shiite group, as well as Hamas in Gaza, with entwined social and military wings that serve as a parallel government.
He has also extended the reach of his Mahdi Army, one of the armed groups that the White House report acknowledged remain entrenched in Iraq. The militia has effectively taken over vast swaths of the capital and is fighting government troops in several southern provinces. Although the militia sometimes uses brutal tactics, including death squads, many vulnerable Shiites are grateful for the protection it affords.
At the same time, the Mahdi Army is not entirely under al-Sadr's control, and he publicly denounces the most notorious killers fighting in his name.
After his Mahdi militia was defeated in a battle against American forces in Najaf in 2004, al-Sadr established himself as a political player, using the votes of loyal Parliament members to give Nouri Kamal al-Maliki the margin needed to win the post of prime minister.
Now that the leadership is in poor repute, al-Sadr has shifted once again. His six ministers in the cabinet and 30 lawmakers in Parliament have been boycotting sessions. They returned Tuesday, but it is not clear they will stay long.
The mainstream political parties in Iraq realize that al-Sadr is growing more influential, but appear to be flummoxed over how to deal with him. They see him as unpredictable and manipulative, but too politically and militarily important to ignore.
"He's powerful," said Jaber Habeeb, an independent Shiite member of Parliament and political science professor at Baghdad University. "This is a fact you have to accept, even if you don't like it."