The devastating death toll has Mr. Peña Nieto, 46, a former governor, promising to move his country’s fight against organized crime in a different direction, focusing more on reducing violence than on detaining drug kingpins. But he has so far offered only vague details of his security plans, focusing instead on social and economic programs.

While Mr. Peña Nieto portrays himself as the leader of a new generation of reformers, he is also a scion of the Institutional Revolutionary Party, or PRI, which ruled Mexico for more than 70 years through a combination of corruption and coercion until it lost power in 2000. During its time in power, the party was known more for keeping the United States at arm’s length while attempting to strike deals with drug traffickers, rather than combating them head on.

Mr. Peña Nieto’s election has brought the PRI back to power, and since so many of those serving in his cabinet have one foot in the past, foreign policy experts who specialize in Mexico say it is not clear where the new government is headed.

“It could go either way,” said Eric L. Olson of the Woodrow Wilson International Center for Scholars in Washington, speaking of future cooperation between Mexico and the United States. “Part of me says, ‘Let’s not assume it’s all going to go south.’ And there are things that are happening that give me hope. But the longer it goes without some clarity, the more doubts creep in.”

Those doubts have also crept to Capitol Hill. Senator Patrick J. Leahy, a Democrat from Vermont who sits on the Senate Appropriations Committee, said he was withholding nearly $230 million in security assistance to Mexico through the so-called Merida Initiative amid concerns about whether the fight against organized crime is doing more harm than good.

“Congress has been asked for a significant new investment, but it’s not clear what the Mexican government’s plans are,” Mr. Leahy said. “It’s premature to sign off on more of the same.”

General García Ochoa, 61, whose background is at once exemplary and enigmatic, personifies that quandary. On paper, he is a model officer. He earned two advanced degrees from Mexico’s most prestigious military academies, and founded the elite National Center for Counter-Narcotics Intelligence. He has been a student and an instructor in American military training programs. He has written three books, including one on the military’s role in the drug fight.