Scenario
America's issues with the Mid East are less pronounced due to a series of events, allowing it to focus on domestic issues.
The Setting
1982 - Ronald Reagan declares his own intensification of the Drug War : This is met with widespread public approval. The USA DEFEND Act (To Defund, Extradite, and Fulfill Enforcement against Narcotic Dealers) is passed, giving the US Federal Government broad powers to arrest, monitor and seize assets. It also authorizes harsh mandatory minimum sentences for low and high level drug offenses.
1986 - Harsh drug policies that do little to curb the demand for drugs cause prison populations to skyrocket. Gangs are quickly gaining money and influence as addicts are forced to choose between prison and addiction. In California, the Bloods and Crips declare a truce to divide the territory of the LA metro area. The Aryan Brotherhood takes a foothold in the deep south. The Northeast a hotbed of competition between the Chinese triads and Italian mafia.
1995 - Incarceration rates are at an all time high. National Guardsmen in the streets of major cities are a common sight, and most police departments now receive surplus hardware from the US military. Texas and California are the first states to experience prison overcrowding, stretching their budgets. Bill Clinton coordinates with the Mexican government to allow the US military and federal law enforcement to conduct operations in Mexico. The dot com boom allows the US to enhance its pervasive surveillance program, but the well funded cartels are beginning to employ crytography to evade law enforcement. The new domain of the drug war is now on the digital front.
2000 - Frustrated with inter-gang violence and the inability of the government to restore order and combat the well equipped cartels, more and more citizens have decided to create militias and vigilante groups. Over 500 of these groups are active, using a variety of legal and illegal weapons acquired through gangs, black market dealers and corrupt government officials.
2006 - The loss in productivity from drug use, mass incarceration, a lack of normalcy and powerful organized crime groups has taken a toll on the US economy. The US inflation adjusted GDP is 9% lower than what it was in 1982. Corruption has become endemic. Several local cops and politicians are feeling the pinch, and are falling under the influence of powerful cartels and whoever has the money. The federal government manages to stay clean, for the most part.
The Question
Fast forward to 2030. How would a criminal gang claim legitimacy in a city that has been under their control for about a year? Said city has transferred control several times in the last 10 years, from the city government, to the federal, and even a few militias. This city is home to 3.5 million people, has a lot of technical and political significance that could help the cartel with it's operations, and is a transit hub that leads to a large suburban population and the Gulf of Mexico.