Executive Summary: We override treaties all the time.
Some folks point to old U.S. commitments to ban marijuana in a series of multilateral treaties as a show-stopper for marijuana legalization. In 1961, the United States agreed to ban it in the Single Convention on Narcotic Drugs, https://www.unodc.org/pdf/convention_1961_en.pdf, so those folks say we shouldn’t change our rules. They list, as an option, this: “If UN antidrug treaties are construed as prohibiting federal legalization, they should be amended to eliminate provisions that produce such a reading.” That’s from Steven B. Duke, “The Future of Marijuana in the United States,” http://law.uoregon.edu/org/olr/volumes/91/2/documents/Duke.pdf.
Amending a treaty with scores of signatories is impractical to the point of impossibility. Are we stuck?
No. We can, we repeatedly and deliberately do, and we should change our internal laws in the face of conflicting treaty obligations that have become or have been proven nonsensical. (We override the treaty by statute; some prefer the terms “breach” or “violate,” but “override” is the tax term.)
First, we can. “An Act of Congress, which must comply with the Constitution, is on a full parity with a treaty, and … when a statute which is subsequent in time is inconsistent with a treaty, the statute to the extent of conflict renders the treaty null.” Reid v. Covert, 354 U.S. 1, 18 (1957).
Second, we do. Working in international tax for Congress years ago, I was involved at the staff level in many treaty overrides via Act of Congress. A long list of U.S. statutes that override international treaties appears in Reuven S. Avi-Yonah, “Tax Treaty Overrides: A Qualified Defense of U.S. Practice,” http://papers.ssrn.com/sol3/papers.cfm?abstract_id=829746. Many of these overrides of international law were loophole closers, completely unobjectionable on policy grounds, except to taxpayers whose loopholes were being closed – and to folks who saw treaties as a higher form of law.
Third, we should, when appropriate. To be sure, treaties are part of the fiber of international relations, and other countries rely on our position. But to view treaties as a higher form of law would allow the President, with consent of a super-majority of the Senate, to adopt unamendable rules — a real box canyon you can enter but never leave. Whether we should change our marijuana laws is a separate issue, but to say we should never violate a treaty goes too far.
Beyond overriding the treaty with reference to marijuana, we could simply — and legally — withdraw, as provided in Article 46, Denunciation. That would get us out of commitments with respect to all drugs, not just marijuana. There’s no violation of international law with that approach.
One more thing: any legal consequences arising out of violating the Single Convention on Narcotic Drugs are so vague and remote as to be nonexistent. Here’s what happens in case of a dispute:
1. If there should arise between two or more Parties a dispute relating to the interpretation or application of this Convention, the said Parties shall consult together with a view to the settlement of the dispute by negotiation, investigation, mediation, conciliation, arbitration, recourse to regional bodies, judicial process or other peaceful means of their own choice.
2. Any such dispute which cannot be settled in the manner prescribed shall be referred to the International Court of Justice for decision.
And the International Court of Justice will do what, exactly?
List of treaties:
The Single Convention on Narcotic Drugs (1961) as amended by the 1972 Protocol
The Convention on Psychotropic Substances (1971); http://www.mesoarch.org/files/convention_1971_en.pdf