In November 2020, 54 percent of South Dakotans approved Amendment A, legalizing the adult use of marijuana. Opposing the outcome of the amendment, state officials initiated a lawsuit arguing that Amendment A violates the South Dakota Constitution’s single‐​subject rule, which restricts amendments to being about only a single subject. A South Dakota circuit judge agreed, striking down the amendment. Now before the South Dakota Supreme Court, supporters of the amendment are seeking to protect the will of the voters.

Over the past half century, states have increasingly rejected federal marijuana policies, recognizing marijuana’s medicinal benefits and the disastrous consequences of criminalizing a plant‐​based substance with no known potential for fatal overdose. And while marijuana legalization may be new territory for South Dakota, the state would not be navigating the transition blindly. Since 1996, states across the country have advanced marijuana reforms nearly every year providing an abundance of examples on how to successfully implement legalization.

That is, of course, how federalism is supposed to work. The Framers of the Constitution created a system where the powers of the federal government are limited and enumerated while the residual powers of the states are much more broad. The Framers understood that the United States was, even then, a vast and diverse country that should not be centrally governed in a homogenous way. Only by giving states considerable leeway to choose local policies would this collection of diverse states be able to live together cooperatively rather than combatively.

Congress disrupted that federal structure with the first federal marijuana law, the Marijuana Tax Act of 1937, and further undermined it with the Controlled Substances Act of 1970. Yet starting in the mid‐​1990s, when the first states authorized medical marijuana, state marijuana laws have changed as local attitudes about marijuana have changed. This hasn’t been uniform, of course, as there are still 15 states that don’t allow even medical marijuana, while 14 states now allow adult recreational use. South Dakota tried to become the 15th state, but legal challenges may overturn the voters’ will.

An overwhelming majority of states that changed their state laws to legalize the adult use of cannabis even did so, like South Dakota, through a citizen‐​led ballot initiative process whereby the state electorate directly chose to enact these reforms. It is this kind of policy experimentation that the Tenth Amendment stands to protect, especially in the face of federal opposition.

When South Dakotans went to the polls, they had long been exposed to the fiscal, policy, and human costs of the state’s marijuana enforcement practices. They voiced their strong support for Amendment A and, as is their legal right, chose to amend their state’s constitution to fully effectuate their will.

Now before the South Dakota Supreme Court, Cato has joined with the DKT Liberty Project, Due Process Institute, and Reason Foundation to file a brief urging the court to reject the challenge to Amendment A and to honor the will of South Dakota’s voters. South Dakota, like all states, is free to experiment with marijuana laws that do not mirror federal law. It has worked elsewhere, and it can work in South Dakota.