The United Nations’ special session on drugs at the General Assembly in New York in April may not have changed anything yet, but the discussions were a long-awaited step toward changes in policies and treaties. (Associated Press file photo)

If the U.S. legalizes marijuana, what happens to its international drug treaties?

"Cannabis is the most vulnerable point in the whole multilateral edifice," said the executive director of the UN Office on Drugs and Crime

When Attorney General Jeff Sessions rescinded a Barack Obama-era federal policy that allowed recreational marijuana to take root in Colorado and Washington, he did more than reignite a domestic legal and cultural battle.

He also highlighted a simmering diplomatic dispute whose outcome will shape U.S. ties with its closest neighbors and its ability to leverage international law: Whether the U.S. will comply with landmark conventions that — largely at Washington’s insistence — unequivocally prohibit recreational use as part of the global fight against drug trafficking.

Notwithstanding Sessions’s lifelong crusade against marijuana, the policy shift is an odd turn of events for an administration that has at least paid lip service to states’ rights and found global governance to be anathema. In effect, it has the U.S. riding shotgun for the folks in black helicopters — only this time, instead of coming for your guns or your taxes, they’re coming for your weed.

The bedrock for the global prohibition against recreational marijuana is the United Nations Single Convention on Narcotic Drugs, which was signed in 1961, entered into force in 1964, and was amended in 1972. (The other two slabs of the global anti-narcotics fundament are the 1971 Convention on Psychotropic Substances and the 1988 Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances.) It classified marijuana as a Schedule I substance, similar to heroin and cocaine. Convention adherents agreed to make its cultivation, sale and purchase for anything other than strictly regulated medical or scientific use a punishable offense — prohibitions codified by the U.S. in the 1970 Controlled Substances Act. More Biblical than therapeutic, the preamble to the 1961 Convention calls the addiction to narcotic drugs “a serious evil for the individual … fraught with social and economic dangers to mankind.”

The preamble’s rhetoric and the convention’s prohibitionist mindset represented something of a victory for the U.S., which spent the 20th century pushing for tougher global drug laws, not least on marijuana. (Never mind its initial mixed motives in going after the global opium trade, or its decision to ignore or encourage drug trafficking, from postwar Burma and Italy to Cold War Afghanistan, when it suited national interests.)

Harry Anslinger, the first commissioner of the U.S. Federal Bureau of Narcotics and one of the U.S. delegation’s leaders, had campaigned against marijuana over his decades-long career. His lurid congressional testimonies read like the screenplay for the 1936 propaganda classic “Reefer Madness.” (Jazz aficionados may also remember him as the official who hounded Billie Holiday, a heroin addict, to her deathbed.) But the convention’s categorization of marijuana on the same plane as heroin and cocaine was based on paltry scientific evidence.

A half-century later, with the evolution of medical research and U.S. public opinion on marijuana, President Barack Obama’s administration tried to paper over the growing contradiction between state efforts to legalize the drug and the restrictions of U.S. law and its international treaty obligations. The Department of Justice’s so-called Cole and Ogden memos set out lenient guidelines for the federal prosecution of marijuana users in states that had legalized its medical and recreational use.

The administration asserted that it nonetheless remained in compliance with the 1961 convention and its follow-on agreements because, in theory anyway, they allowed some degree of flexibility and prosecutorial discretion. The International Narcotics Control Board, the body in charge of monitoring treaty compliance, has repeatedly rejected that argument, noting that the convention explicitly prohibits any non-medical use of marijuana. More recently, it dismissed any idea that federalism offers any leeway to countries in upholding the convention’s obligations.

This dispute transcends purely legal arcana. The UN drug conventions are among the world’s most widely adhered legal instruments. As David Johnson, a member of the INCB and the former assistant secretary of the State Department’s Bureau of International Narcotics and Law Enforcement Affairs (aka “Drugs & Thugs”), told me, “The U.S. has a strong interest in preserving respect for international law, and the current situation makes it more difficult for the U.S. to be a clarion on this issue.”

The U.S. is no stranger to exceptionalism — it hasn’t ratified popular international treaties such as the Law of the Sea, for instance. But in this case, the U.S. isn’t just standing aside from a treaty. It’s flouting a convention that it orchestrated and ratified.

That glaring hypocrisy is particularly corrosive in its hemisphere, where 17 countries considered “drug majors” undergo an annual U.S. certification process that includes judging their willingness to eradicate the cultivation and trafficking of cannabis. When the INCB jumped all over Uruguay for its recent legalization of recreational marijuana, its president, Jose Mujica, tartly rejoined, “Do they have two discourses, one for Uruguay and one for those who are strong?”

Latin American societies remain deeply conservative, and public opinion toward marijuana is shifting more slowly than it has in the U.S. But shifting it is. Several Latin American nations now allow the medical use of marijuana, Caribbean countries are considering the ramifications of legalization, and the Mexican Supreme Court ruled in November 2016 in favor of some individuals’ recreational consumption, to cite a few recent examples of concern to the INCB in its most recent report. As Johnson pointed out, those decisions reflect each country’s domestic circumstances. At the same time, what the U.S. does can cast a long shadow. It’s pretty hard to tell Mexico to crack down on pot growers and wholesalers when California has legalized those businesses.

Sessions’s prohibitionist crusade — as he put it, “Good people don’t smoke marijuana” — seems unlikely to go far. More than 50 percent of all Americans 18 and over have tried marijuana; and more than 50 million Americans use it. That’s a lot of bad people to put in the hoosegow. If anything, as John Walsh of the Washington Office on Latin America told me, “The attempt to turn back the clock will hasten the day that Congress gets its act together and modernizes U.S. laws on cannabis.”

But that would just aggravate the U.S.’s international law problem. Opening the convention for renegotiation or amendment would be tricky and difficult, not least because of potential resistance from prohibition-minded China, Russia and African nations. Yet allowing states that have legalized marijuana to keep blowing smoke about their adherence to the convention risks undermining all the drug conventions, which remain vitally important for controlling truly dangerous drugs. As the executive director of the UN Office on Drugs and Crime put it, “Cannabis is the most vulnerable point in the whole multilateral edifice.”

Outlining a series of options, Walsh leans toward what he and others call “principled noncompliance.” Instead of clinging to dubious legal arguments, nations that choose to legalize marijuana should fess up to not abiding by the convention, explain their rationale, and attempt to mobilize other like-minded states in a reform effort. This approach, he argues, is less disrespectful of international law because “it confirms that treaty commitments matter.”

Would such an approach work? We may be about to find out. In fulfillment of a campaign promise made by Prime Minister Justin Trudeau, Canada is moving to legalize marijuana by this July. Doing so will put it clearly out of compliance with the 1961 convention and squarely in the INCB’s sights. Proud of its global good citizenship, Canada has a strong incentive to find some way to square the circle. What it does will “provide a preview of how these drug treaty tensions might be managed,” says Walsh.

Granted, only a tiny subset of the 50 million smokers back in the U.S. may have thought about this wrinkle. But those who care about international law and the soft power that flows from it should keep their eyes on their northern neighbor. For the world’s marijuana smokers, what happens in Ottawa may not stay in Ottawa.

Gibney writes editorials on international affairs for Bloomberg View. He was features editor at the Atlantic, deputy editor at the New York Times op-ed page and executive editor at Foreign Policy magazine. He was a foreign service officer and a speechwriter for Secretary of State Warren Christopher, National Security Adviser Anthony Lake and President Bill Clinton.

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