Gary Johnson is now the only* GOP presidential candidate whose policy position on U.S.-Mexico relations does not involve predator drones or unassailable walls. Instead, the former two-term New Mexico governor made the case in a Washington Times op-ed and again on his "Truth for a Change" blog that border violence is tied to–gasp–drug trafficking:

The border war is not an immigration problem—illegal or otherwise—and even if it were, fences and troops would not solve it. If anything, the crackdown measures of recent years, while doing little or nothing to address illegal immigration, have had the unintended consequence of upping the ante for the cartels trying to move drugs across that same border, resulting in greater crime and violence. Immigration is a different issue—and one that must be addressed not with fences, but with a system for legal entry and temporary work visas that works. Real border security is knowing who is coming here and why. Border violence, on the other hand, is a prohibition problem. Just as we did for Al Capone and his murderous colleagues 90 years ago, our drug laws have created the battlefield on which tens of thousands are dying. By doggedly hanging onto marijuana laws that make criminals out of our children while our leaders proudly consume wine at state dinners, we have created an illegal marketplace with such mind-boggling profits that no enforcement measures will ever overcome the motivation, resources and determination of the cartels. There are ample reasons why millions of Americans, the Global Commission on Drug Policy and, just recently, former Mexican President Vicente Fox are calling for legalization of marijuana as an alternative to the failed and ridiculously costly "war on drugs." Twenty-eight thousand deaths along the border are certainly among those reasons. Will legalizing marijuana put the criminal cartels out of business? No. But it will immediately deny them their largest profit center and dramatically reduce not only the role of the United States in their business plans, but also the motivation for waging war along our southern border.

National marijuana legalization in the U.S. would probably mitigate border violence, but notice Johnson's caveat: It won't put cartels out of business. The broadest plan on the table, proposed in June by Reps. Barney Frank and Ron Paul, only repeals federal prohibition of the drug, meaning that cartels would still have black markets in the nearly three dozen states that don't even have medical marijuana.

The other problem is that while weed may provide up to 60 percent of their revenues, the cartels also make and sell meth, and coordinate and protect shipments of cocaine coming from South America. Within Mexico, the cartels are engaged in many of the forms of organized crime that plagued the U.S. long after alcohol prohibition was repealed. To say that they'd lose interest in the U.S. if we legalized marijuana is, I think, to severely underestimate their flexibility and interest.

In terms of broader geopolitical questions, Mexico and many other Caribbean/Central American countries have attempted to reorganize their military and police around drug warring as part of the Merida Initiative. What happens when we admit that was all a huge, stupid mistake?

*A reader points out that Huntsman is also good–from a liberty perspective–on immigration.