They also get credit for most of the good in the area - whether they're responsible or not. The US military has just embarked on a multimillion dollar effort to improve Sadr City's sewage and water supply, but most residents, when asked who's responsible for the earthworks on many streets, say it's being done by the Mahdi Army.
The modest lifestyle of the Mahdi Army's leaders - as well as their past and present involvement in operations against Saddam Hussein, US forces, and criminals - gives them enormous street credibility in this tough neighborhood.
"The Sadr family has lived with the people and suffered with us,'' says Salam Abeid Kassim, a policeman lounging in a Sadr City tea shop. "All of these exiles who the Americans put in charge - we can't respect them. The Mahdi Army are the only ones working for us."
Sadr's father, Mohammed Sadek al-Sadr, was assassinated in 1999 along with two of his sons for speaking out against Saddam Hussein. His uncle, Mohammed Bakr al-Sadr, was killed by the regime in 1980. To supporters, that legacy gives the family's most prominent descendant the moral right to speak and to lead over former exiles like the secular Shiite Ayad Allawi, the interim prime minister who left Iraq in 1975.
To be sure, it's hard to know if all the glowing reviews given to the Mahdi Army from dozens of people in Sadr City are genuine, since the organization's members are rarely out of earshot. Inside the Mahdi Army, members are kept strictly on message by regular communiqués from Sadr's office that stresses the chain of command and warns them off taking any action unless officially authorized to do so.
Nevertheless, the veneration and support for the group seems genuine, nowhere more so than at the Waiting for the Mahdi Mosque, where 40 boys between the ages of 10 and 12 are undergoing religious instruction from a Mahdi Army member.
They eagerly raise their hands when asked questions about basic Shiite religious practices, but get really worked up when their teacher says they can reenact the Mahdi Army's first clash with American forces. That was in August last year, when US soldiers in a helicopter tried to remove a Mahdi flag from a communications tower, prompting an outburst by Sadr supporters. US forces, taking fire from a crowd, shot back and 13-year-old Wael Ayman was killed.