Some Washington policy makers are concerned about the new approach. Representative Henry Cuellar, a Texas Democrat who was with Mr. Peña Nieto on election night on Sunday, said he advised the Peña Nieto camp to make an emphatic statement rejecting any sort of deal with criminals to calm the apprehension some members of Congress feel about the PRI’s resurgence. “I told his people to be very clear, there will be no truce or approval of cartels,” Mr. Cuellar said.

Mr. Peña Nieto has done just that, repeatedly.

In a sign of his commitment to the drug war, he has also hired Gen. Óscar Naranjo, the former head of Colombia’s national police, who helped the United States take down the cocaine kingpin Pablo Escobar. Beyond that, Mr. Peña Nieto’s long-term proposals include expanding the federal police, helping prosecutors create special offices to focus on crimes like murder and kidnapping and creating a 40,000-person “gendarmerie” for policing rural areas.

But in the meantime, analysts expect Mr. Peña Nieto to continue the aggressive, militaristic approach of President Felipe Calderón. “To close that credibility gap, he will need to “out-Calderón Calderón,” said Alejandro Hope, a former Mexican intelligence official.

That could mean what some analysts are predicting will be a “surge” not unlike the 2007 American troop increase in Iraq. It would be defined by the Mexican government rapidly increasing the law enforcement and military resources assigned to specific states or cities that are struggling with violence and crime.

The vote count, however, suggests that Mr. Peña Nieto could face some constraints and a difficult choice of location. He lost the two most violence-racked border states, Tamaulipas and Nuevo León, and he nearly lost Veracruz, another state where violence has recently skyrocketed. Moving a lot of soldiers into one of those states, or reassigning resources from another one, would probably anger residents who already oppose the PRI.

Mr. Hope adds that Mexico’s federalist system means Mr. Peña Nieto will probably have to pay a hefty price to state and local leaders to persuade them to introduce any new security plan, possibly with expensive programs or infrastructure. Some analysts worry that putting the Peña Nieto security plan in place, along with other efforts to fulfill campaign promises, will bring an end to the fiscal restraint of the past decade.

“There is going to be a general opening of the purse strings,” said Duncan Wood, a political analyst and a professor at the Autonomous Technological Institute of Mexico.