Yesterday, the attorneys general of Nebraska and Oklahoma filed a complaint asking the U.S. Supreme Court to declare Colorado’s Amendment 64, which legalized marijuana for adults, unconstitutional.

The gist of the complaint is that federal law prohibits possession of marijuana and that Colorado law “conflicts with and stands as an obstacle to the full purposes and objectives of” the federal government. Thus, the argument runs, Colorado’s Amendment 64 violates the Supremacy Clause of the Constitution and should be declared invalid. Unlike, say, Maine or Hawaii, Nebraska and Oklahoma border Colorado and claim they suffer substantial and irreparable harm from Colorado’s new policy on marijuana. (Some residents of Nebraska and Oklahoma would rather drive across the border and buy weed legally in a store rather than engage in a criminal black market transaction closer to home. This cross-border activity upsets the authorities in both states, prompting the lawsuit.)

Will the Supreme Court accept this case for review? That’s impossible to predict. However, the constitutional argument being advanced by Nebraska and Oklahoma is weak and so would likely fail. Just because the federal government enacts a law against marijuana, it does not follow that all the states have to enact laws against marijuana. And just because the federal police (FBI and DEA) have grown accustomed to having state and local police conduct marijuana raids and arrests, it does not follow that the local authorities can’t stop doing that. So long as the local police are not arresting or threatening to arrest federal agents for trying to enforce the federal law, there is no “conflict.” Thus, the Supremacy Clause does not come into play.

Here is an excerpt from a Cato paper by Robert Mikos on this subject:

The American Constitution divides governmental power between the federal government and several state governments. In the event of a conflict between federal law and state law, the Supremacy Clause of the Constitution (Article VI, Clause 2) makes it clear that state policies are subordinate to federal policies. There are, however, important limitations to the doctrine of federal supremacy.

First, there must be a valid constitutional basis for the federal policy in question. The powers of the federal government are limited and enumerated, and the president and Congress must always respect the boundary lines that the Constitution created.

Second, even in the areas where federal authorities may enact law, they may not use the states as instruments of federal governance. This anticommandeering limitation upon federal power is often overlooked, but the Supreme Court will enforce that principle in appropriate cases.

Using medical marijuana as a case study, I examine how the anticommandeering principle protects the states’ prerogative to legalize activity that Congress bans. The federal government has banned marijuana outright, and for years federal officials have lobbied against local efforts to legalize medical use of the drug. However, an ever-growing number of states have adopted legalization measures. I explain why these state laws, and most related regulations, have not been—and cannot be—preempted by Congress.