When 2,500 army troops took the place of police officers on Mexico City streets this month, it was only the latest move by President Ernesto Zedillo to put internal security in the hands of the military.
Citing spiralling crime, drug trafficking and corruption within the police, Mr Zedillo had already appointed army officers to head key civil jobs - the Mexico City police, the Federal Judicial Police and the Anti-Narcotics Institute.
When the general appointed last December to head the latter was arrested last month for protecting a major drug cartel, questions were raised over Mr Zedillo's logic.
Since the 1910-17 revolution, the Institutional Revolutionary Party (PRI) has maintained an unwritten pact under which the military retains virtual autonomy in return for staying out of politics. Now, many Mexicans fear the military could be getting a taste for power.
"Bringing in the military to replace the police sets a dangerous precedent," said political analyst German Plascencia of the Iberoamerican University in Mexico City. "It is part of moves by the state to defuse social mobilisation around the country. Such active participation by the army gives its officers ideas and power. It could lead to a coup d'etat."
"There is a risk that a stronger military presence in civil affairs will lead to a greater use of force," said Clemente Valdez, an expert on the Mexican constitution. "That can erode civil liberties and lead to more violence."
With the capital's police force renowned for its corruption, Mr Zedillo appointed General Enrique Salgado to head the city force last year. The generalkicked out scores of police officers and brought in his own men.
Mr Zedillo then named General Tito Valencia Ortiz to head the Federal Judicial Police. Then came the appointment in December of General Jose Gutierrez Rebollo to head the National Institute for the Combat of Drugs. Last month, however, General Gutierrez was detained for allegedly being in cahoots with drug baron Amado Carrillo.
Last month, Mr Zedillo sent soldiers to replace Federal Judicial police in his home state of Baja California, apparently because the police force was protecting drug shipments across the border to the US.
And this week, 2,500 soldiers fanned out across the crime-ridden Iztapalapa district of the capital. The official version was that the 3,000 police officers were being sent on a military-style training course to equip them to fight spiralling crime. Similar job swaps are planned through the capital.