Mexico's drug cartels depend on smugglers to move their illicit wares. But to listen to the U.S. Border Patrol, you'd get the impression that most of the smugglers are Mexicans. In fact, most are born-in-the-USA Americans, as the cartels prefer that their mules look like Walter White. And the Border Patrol knows it.

According to the Center for Investigative Reporting (CIR), U.S. citizens comprise the overwhelming amount of drug-related arrests in recent years by the Border Patrol. They're about 80 percent of the total, according to arrest data acquired by the group.

Authors Andrew Becker, George Schultz and Tia Ghose don't dispute that Mexican drug cartels are in control of the drug smuggling trade. "But the public message that the Border Patrol has trumpeted for much of the last decade, mainly through press releases about its seizures, has emphasized Mexican drug couriers, or mules, as those largely responsible for transporting drugs," they write.

This impression was reinforced by Customs and Border Protection spokesman William Brooks, who told the CIR that the "majority of people involved in smuggling drugs are citizens of Mexico." Thirty-eight percent of the time, press releases from the agency announcing an arrest notes a Mexican nationality, according to the authors. When it's a U.S. citizen, the number drops to 30 percent.

The authors refuted the Border Patrol's claims by sifting through the agency's own data. For the 40,000 drug arrests counted by the Border Patrol between 2005 and 2011, "at least one U.S. citizen was involved 80 percent of the time," according to CIR, citing data acquired from the border watchers through the Freedom of Information Act.

When the data is selected to include just arrests for drug trafficking – or large amounts of drugs intended for re-sale – instead of simple possession, U.S. citizens make up two-thirds of the total.

So some U.S. citizens arrested at the border for drugs, like Snoop Lion and Willie Nelson, are simply being busted with their personal stash. Leave out marijuana and include only hard drugs like cocaine and methamphetamine, the number drops to 60 percent.

Though the authors note the data isn't comprehensive. The total number of drug seizures is double the total number of arrests. Many drug seizures are reported after a suspect fled and escaped, with no arrests counted.

As for why Americans are turning to drug smuggling (the share of U.S. citizens is increasing, according to the report) the authors believe it's due to a combination of factors. There's the Walter White scenario from Breaking Bad: being driven into the illicit drug trade by economic desperation. But few have the fictional White's experience and street smarts, and are often caught the same day or week they're hired.

The CIR interviewed one former trafficker who said the cartels seek out U.S. citizens – particularly of middle-age – because they're less likely to draw suspicion. Police officials believe the cartels are hiring more drivers to smuggle smaller loads instead of big ones, reducing the chance of a major bust but requiring more people. It's also an easy trade to get into. Friends and relatives might do it, or classmates or coworkers. In sum, it amounts to a kind of de facto social safety net for many people living along the border.

This isn't to deny that the cartels are seriously bad, and perhaps the drug smugglers from Mexico are simply escaping capture. U.S. citizens have fewer places to run than a Mexican citizen who can more easily flee across the border. On the other hand, at these rates, the cartels likely wouldn't be as powerful as they are without the growing number of Americans who willingly work for them.