At the time of his election, Mr. Calderón’s biggest challenge seemed merely to establish his constitutional authority, which AMLO refused to recognize by naming himself the “legitimate president” and trying to bring Mexico City to a standstill through a series of mass rallies. But Mr. Calderón had the sense to let those rallies burn themselves out. Instead, within days of taking office he mobilized the Mexican military for an all-out war against the drug cartels.

Since then, some 55,000 Mexicans have been killed, most of them members of rival cartels but also some 1,000 children, close to 100 mayors and dozens of reporters. …

“When I took office,” he says, “I could see twin processes. On the one side you could see the [law enforcement] agencies, mainly the police corps, absolutely penetrated by corruption and in a very dangerous weakening process. And, on the other side, empowerment of criminal organizations. . . . Today we have the trends the other way around.” …

Mr. Calderón cites a number of obstacles, one of them being constraints that Mexico’s federalist system puts on his presidential powers. “The director of the national police of Colombia could remove any single officer,” he says, pointing to a country often compared with Mexico. “However, if I, as president, see there is a cop in the corner getting bribes, if I do not have enough judicial evidence, I do not have the capability to remove him.”