This morning the Supreme Court declined to take up a lawsuit by the states of Nebraska and Oklahoma challenging Colorado’s Amendment 64 measure that legalized the sale and use of marijuana. Not just medical marijuana, but recreational use as well.

We detailed the arguments involved in the case last year:

The Nebraska/​Oklahoma argument: because the federal government, through the Controlled Substances Act, has banned marijuana, states are not allowed to contradict that ban by creating a regulatory framework for legalization. Further, Colorado’s official regulation of recreational marijuana imposes a nuisance burden on surrounding states due to an alleged increase in drug trafficking. While Nebraska and Oklahoma disclaim any intent to force Colorado to “re-criminalize” marijuana, the suit argues that Colorado’s official efforts to regulate the legal marijuana industry bring the state into conflict with federal and international drug laws.

Colorado’s response: there is no conflict. Federal marijuana prohibition is still in effect, and the decision not to prioritize enforcement in states that legalize marijuana came from the federal government, not Colorado. If Nebraska and Oklahoma object to the manner in which the federal government is discharging its law enforcement duties in Colorado, they should be suing the federal government. Colorado’s regulation of the marijuana industry is within its prerogatives under the CSA. As to the nuisance claim, Colorado argues that mere policy differences between states that don’t directly injure the sovereignty of other states are not actionable nuisances.

The legal basis for the lawsuit has been questionable from the beginning, with legal commentators both challenging its merits and pointing out the irony in two of America’s “reddest” states taking a legal posture that overruns state sovereignty in favor of federal power.

And, of course, if prohibition states are concerned with the costs, they could always legalize and regulate marijuana themselves and spare their justice systems the immense costs of prohibition.

Today’s result is not surprising, especially after the Obama Administration urged the court to decline the case, and the outcome fits with our analysis of the case’s prospects in 2014:

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.

Today’s action at the Supreme Court amounts to a big boost to the marijuana legalization movement, which continues to gather strength and momentum.

For those interested in a deep dive into the legal issues, check out the Cato Policy Analysis by Robert A. Mikos, On the Limits of Federal Supremacy: When States Relax (or Abandon) Marijuana Bans.