The diplomatic missives released by Wikileaks last week show that the U.S. was quietly dismayed by Mexico's inability to dismantle its powerful cartels. But they also give deeper insight into the role that U.S. intelligence has played in Mexico -- and some concern that rival political parties can change that.

The 2,800 cables between American diplomats reveal the depth to which American intelligence helped in the capture of some of Mexico's drug lords. But they also show a concern that the former ruling party, the Institutional Revolutionary Party or PRI, may make a comeback.

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Mexican President Felipe Calderon.

American law enforcement has worked in Mexico for decades, but they haven't enjoyed the access they have now until President Felipe Calderón took office. Buried in the dispatches disseminated by Wikileaks activists are messages from top embassy officials, worried about the rise of the PRI and a return to an older way of doing things.

For more than 70 years, the PRI held power in Mexico. It weakened dramatically in the 90s amid accusations that its presidents and generals were in the pay of the Juárez Cartel.

And now, just as the American embassy feared in those messages a year ago, the party is rising again. Last summer, the PRI won nine of the twelve gubernatorial seats in the country. This week, a major Mexican newspaper released a poll. They show voters favor the PRI for 2012's presidency.

"I think that there's a real sense of apprehension on the part of U.S. authorities about the possibility of political change in 2012 in Mexico, particularly the idea that the PRI, the old ruling party, would return to power," said David Shirk, director of the Trans-Border Institute at the University of San Diego.

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Photo: family photo

Cartel leader Arturo Beltrán Leyva was killed by the Mexican government acting on American information, according to documents released by Wikileaks last week.

Even in the middle of a war that's decimated regions of Mexico, there's been some successes, key arrests of some of the most savage players. In the past year, acting on American information, the Mexican government killed Arturo Beltrán Leyva, a rival to the Sinaloa Cartel. Then it arrested "El Teo" Garcia in Tijuana. Its most recent victory: Tony Tormenta, a high profile leader within the Gulf Cartel.

Andrew Seeley, director of the Mexico Institute at the Woodrow Wilson Center, says the intelligence sharing was crucial to those takedowns.

"We're seeing a lot of this right now in Ciudad Juárez, we're seeing it in the border cities in Sonora, near Arizona, in Tijuana, lots of intelligence sharing – but also inside Mexico, where the U.S. government often has very good intelligence on some of the top leaders of the cartels they're able to share with their Mexican counterparts so they can locate them," Seeley said.

Another dispatch criticizes the Army as a blundering holdover of the Mexican revolution. John Bailey, a Georgetown professor who works in Mexico, says the Mexican Army proved a poor choice for engaging the cartels.

"The army is a big hulking bureaucracy that doesn't respond very well to the kind of police operational intelligence," Bailey says. "So the Americans are turning more to the Mexican Marines."

Carlos Pascual, the U.S. ambassador to Mexico, has said the Wikileaks "illegal disclosure" will not hurt relations between the two countries.

Read the Wikileaks cables about Mexico in Spain's El País newspaper.