When Mexican President Felipe Calderon declared war on drug cartels in 2006, he summoned his military to serve as the tip of the spear.
Since then, nearly 50,000 uniformed Mexican military personnel have manned roadblocks, patrolled cities haunted by drug killings and raided houses in search of traffickers and contraband.
But as doubts mount over the effectiveness of Calderon's anti-drug crusade, with its death toll of 18,000 people, so do the political risks for Mexico's military, traditionally one of the nation's most trusted institutions.
Brig. Gen. Benito Medina has indicated that the Mexican military cannot succeed alone against a powerful foe whose reach spans national boundaries.
"We need the collaboration of the international community," Medina, director of military education at the University of the Army and Air Force, said in remarks published Monday in El Universal newspaper.
The United States, as part of its $1.4-billion multiyear Merida Initiative, is sending Defense Secretary Robert M. Gates, Adm. Michael G. Mullen, chairman of the Joint Chiefs of Staff, and Homeland Security Secretary Janet Napolitano to accompany Secretary of State Hillary Rodham Clinton in Mexico on Tuesday for talks on the country's drug war.
The Mexican army is increasingly a lightning rod for those who say the Calderon strategy has failed to curb a skyrocketing death toll. Human rights advocates accuse soldiers of abusing residents as they hunt drug traffickers. And there is a growing feeling that, despite the army's firepower and resources, it has been less than effective as a police force.
Street demonstrations against runaway violence in the border city of Ciudad Juarez aimed more vitriol at troops than at drug-trafficking gangs, and many residents say they would like to see soldiers called back to the barracks. As the military's presence has grown along the U.S.-Mexico border, many residents ask whether it will prove as susceptible to corruption as the police have been.
"If the fundamental institution of any state, the armed forces, can't prevail in the battle against narco-trafficking, then what is next?" asked Jose Luis Pineyro, an expert on national security at Mexico City's Autonomous Metropolitan University. "It is the last recourse."
Mexico's 250,000-strong armed forces -- an army, navy and air force -- enjoy high esteem nationwide, despite modest signs of slippage during the three-plus years of the drug war.
The military ranks third among the most trusted institutions in Mexico, behind the Roman Catholic Church and higher education, according to a survey published in January by the Mitofsky polling firm. A year earlier it was first.
Another poll last year, by Demotecnia, showed that 72% of Mexicans view the army favorably, though the most recent figure represents an 11% drop since 2007.
Mexico's human rights commission has received more than 3,400 complaints of alleged violations, including torture and unlawful detention, by military personnel since December 2006, when Calderon took office. Defense officials say the commission has recommended disciplinary action in only a small fraction of those cases, but the military's hermetic legal system makes it difficult to track how they turned out.
Calderon has acknowledged the military's limitations. In Ciudad Juarez, where a turf war has killed more than 4,000 people since 2008 despite the presence of 10,000 troops and federal police, the Mexican president promised fed-up residents to retool his drug war strategy to aim more of the government's attention at jobs and living conditions.
Most Mexicans support using troops in anti-drug operations, though the margin has shrunk since two years ago. Given rampant police graft, especially at the state and local levels, soldiers are seen as the most reliable force to take on heavily armed drug gangs.
The drug war has boosted the military budget and created an opportunity for the armed forces to gain clout.
"If they win, they will be stronger politically," said Raul Benitez, a specialist in national security at the National Autonomous University in Mexico City. "They think they will win."
Yet the deaths related to drug traffickers and the government's failure to land a decisive blow against the cartels has many Mexicans questioning the effectiveness of the military-led strategy. And military leaders, who have never appeared eager to join the drug war, are concerned that they could end up bearing the blame, analysts say.
"They have made it really clear that they take orders from the civilian leadership," said Roderic Ai Camp, an expert on the Mexican military at Claremont McKenna College.
Napolitano irritated Mexican officials last week when she appeared to question the military's effectiveness in Ciudad Juarez. Her comments came after the fatal shootings of three people connected to the U.S. Consulate there.
"President Calderon of Mexico has been deeply involved, even sending in the military into Juarez. That hasn't helped," Napolitano said during an interview on MSNBC.
Fernando Gomez Mont, Mexico's interior secretary, fired back, saying troops are filling an important law enforcement role while the government rushes to clean up and rebuild police forces. He said troops would stay as long as needed.
The military has delivered some of the Calderon government's biggest blows against drug traffickers.
In December, Mexican marines shot and killed kingpin Arturo Beltran Leyva during a raid on an apartment complex in the city of Cuernavaca, south of Mexico City.
A marine died in the operation and, hours after his publicized burial, four of his family members were killed by gunmen in apparent retribution for Beltran Leyva's death.
Mexican troops have captured other high-profile figures. In the past, leaks from crooked police often allowed suspects to escape before authorities arrived.
Mexico's military has never had such a prominent anti-drug role. Once mainly limited to hunting and destroying crops of poppy and marijuana, troops now field tips, sift intelligence, search alleged safe houses and round up suspects.
Critics of Calderon's anti-drug strategy complain that those are tasks military forces were never properly trained to perform.
"They are put in a situation they are not prepared for, and they commit errors that further hurt their image," said Manuel Espino, a former president of Calderon's National Action Party who charged that using the military for police work subjects it to "unnecessary risk."
It remains unclear how long military personnel will continue policing the streets as part of the drug war.
"Nobody wants this fight to go on indefinitely," Gen. Guillermo Galvan Galvan, the defense secretary, said during an Army Day ceremony last month. "It is in no one's interest."
Times staff writer Tracy Wilkinson contributed to this report.