The tipping point where we can no longer regain control over Iraqi violence is, in part, when Iraqis assign greater legitimacy to the sources of violence than to the pro-American forces trying to quell them.

We're getting close:

Behind the maze of men with guns in Iraq is a very simple truth: their barrels offer protection, something Iraqis say the government has never given them.

Iraq is awash in killings, and many are blamed on the Mahdi Army, the militia commanded by a glowering Shiite cleric, Moktada al-Sadr. The cleric controls a large and crucial bloc of seats in Parliament. At the same time, 92 percent of the mortar and rocket attacks in August and September on the Green Zone — the protected area in Baghdad that houses the American military and the Iraqi government — came from Sadr City.

As the recent fighting in Amara shows, the group and its rogue elements have settled deeply into the crevices of Iraqi society, filling college security offices and student unions, as well as the ranks of the police and the army. It is often at the center of spasms of sectarian killing, like the violence last weekend in Balad, and it frequently battles rival Shiite groups, as in Amara, and earlier this month in another southern city, Diwaniya. ... [I]t is impossible to tell where loyalties to Mr. Sadr end and criminal activity begins. Rogue groups of his former followers now run underground fiefdoms of sectarian killing and kidnapping — and even a special market for victims’ cars. One of his senior aides was arrested by the American military earlier this week on suspicion of having directed the killing and torture of Sunnis. The Americans later reluctantly released him at the request of the Iraqi government.

The mechanisms for killing have become more sophisticated. A senior coalition intelligence official at a briefing last month detailed an example of a Mahdi Army death squad. Group leaders are issued instructions on order forms listing a target person and an address, the official said. A group can consist of special forces, intelligence units and punishment committees, complete with clerics who impose sentences. Some of the leaders may be inside the Interior Ministry, the official said. Others may work with their contacts within the ministry to obtain equipment such as cars.

The Mahdi Army’s victims are sad, struggling figures, often stuffed into the trunks of cars. This tactic became so widespread that Iraqi soldiers at checkpoints have been known to stop cars that are playing loud, thumping music, mistaking the sound for a person trying to get out.

In the eastern Baghdad neighborhood of Ur, which is connected to Sadr City by a fast and largely empty road, a worker counted 14 victims on a particularly bad day in August, shortly after an attack on a procession of Shiite pilgrims. He said four were shot in front of him on a dirt road near a high school. The bodies of another 10 were dumped there later that day. Police cars, like hearses, later picked them up.

The killing took place openly, often silently, and without fanfare. Gunmen did not bother to hide their faces. One resident sardonically referred to Ur as gbour, which means graves in Arabic.

Iraqis began referring to the victims, often Sunnis, as sheep. Most condemn the killing, which they attribute to the Mahdi militia.

“I know they are killing Sunnis now — none of us likes this,” said Firas al-Saeidi, a 29-year-old Shiite resident of Sadr City, who works in the Ministry of Defense. “But it keeps balance in our sensitive areas. We need that.”