Perhaps the most dangerous group of narco-assassins in Mexico looks to be reeling a bit from recent setbacks. One of the ironies of the poor health of the Zetas? Drug trafficking across the border is going up.

A DC-based human rights group, the Washington Office on Latin America, describes the Zetas' control as "slipping a bit" – but they're not celebrating. "This is an ominous bit of news," write Adam Isacson and Maureen Meyer, "if a vacuum or organized crime control has opened up, violence may flare up again in Northeastern Mexico." Not only is U.S. border security "not deterring traffickers," heroin busts are up – and police are seeing an increased flow of potent liquid methamphetamine, a reportedly more efficient way to transport the drug.

The Zetas' kingpin, Heriberto Lazcano, was killed by the Mexican military in October. The reportedly more violent drug lord Miguel "Z-40" Trevino has since taken Lazcano's place, and the cartel has experienced a violent internal conflict along with attacks by their rivals: the Sinaloa Cartel. Isacson and Meyer also suggest that a sign of the turmoil is how drug smuggling routes previously "locked down" by the cartel have opened up, giving other criminal groups an opportunity to sneak drugs into the U.S. while slipping past the Zetas.

The authors are cautious about the extent to which the Zetas are really on the ropes, and note that the cartel remains strong. Another question is where the Zetas are losing control, more precisely. According to Mexico City newspaper Reforma, homicides in five of six of Mexico's border states declined in 2012. A strict crackdown on kidnappers by the police and army have been suggested as one reason for the decline in violence in cities like Ciudad Juarez. Another theory has it that the Sinaloa Cartel, the Zetas' main rivals, eliminated or sidelined smaller rivals like Juarez's street gangs.

The exception is the border state of Coahuila. Unlike other Zetas strongholds, rates of violence in the state have shot upwards. Coahuila's largest city, Torreon, has seen enough rising violence for El Manana to label it "the most violent of Mexico," with numerous attacks in recent weeks on bars, nightclubs, drug rehabilitation clinics and military checkpoints. "Those are results, basically, of clashes between the Zetas and Sinaloa," Christopher Wilson, a Mexico analyst with the Woodrow Wilson International Center for Scholars, tells Danger Room. "Maybe not entirely, but that's the driving force behind that violence. The Zetas' position in certain areas may be being threatened right now."

Wilson cautions, though, that there's not been a corresponding increase in violence in states that are firmly under the control of the Zetas. This "makes me think that they're not on the verge of extinction or anything close to that," Wilson adds. Earlier in January, the Dallas Morning News' Alfredo Corchado, citing law enforcement officials, reported that the Zetas were pushing further into Coahuila, "threatening to reignite deadly violence in areas bordering Texas." One estimate of homicides in Mexico touted by the Mexican news media counted more than 1,000 deaths since the first of December, "a pace even faster than during the administration of [President Enrique Pena Nieto's] predecessor, Felipe Calderon," Corchado wrote.

That's a problem for Mexico's new president. Pena Nieto has emphasized reducing violence as an alternative to a blunt-force attack on the cartels of the kind deployed with gusto by Calderon. Wilson and his colleagues at the Mexico Institute have written that the shift in strategy – likely in the form of targeting kidnappers and extortion rings – could be a "positive first step," but expressed concern that the president hasn't clearly described it. The talk around the new strategy also came during an election year, and just before the news that the Pentagon is expanding its assistance to elite units within the Mexican military.

"The government of Mexico describes its use of the military as a stop-gap measure, while longer-term efforts are put in place," Wilson says. "Well, I think sort of the question is: what are the long-term efforts?" They may not come soon enough before the Zetas bounce back.