Democratic presidential candidate Sen. Bernie Sanders, I-Vt., speaks during a primary night election rally in Essex Junction, Vt., Tuesday, March 3, 2020. (AP Photo/Matt Rourke)

Sen. Bernie Sanders has long been an advocate of cannabis legalization. He and Sen. Elizabeth Warren are the only two remaining candidates in the 2020 presidential campaign who vocally support federal legalization. Sanders has repeatedly said that, if elected, he’d sign an executive order on his first day in office to legalize cannabis in all 50 US states.

That promise makes a rousing line in a stump speech. But could he really do it?

Unfortunately, it’s not so simple.

A Sanders administration would almost certainly mean a step forward for cannabis policy in the United States. But it’s virtually impossible for any president to sign a document on Day 1 that would immediately legalize cannabis throughout the country. Our federalist system of government simply doesn’t work like that.

How to legalize cannabis in the US

There are two general paths to legalizing cannabis under federal law. Either Congress can pass a bill and the president can sign it into law—in which case having Sanders or Warren in office would definitely help this along—or the executive branch can deschedule cannabis administratively.

The first path, via Congress, is by far the simpler method. Federal lawmakers pass a bill that says, essentially: “All that stuff we said about cannabis being illegal? That’s gone. Here’s what we’ll do instead.”

Even that is no easy task. Not only do you have to convince Congress to pass a bill, but then you have to set up a system to regulate the plant and its products nationwide. As we’ve seen the ongoing federal effort to figure out how to regulate CBD, it could be years before a framework for legal interstate sales might be complete.

Let’s say you do all that. Congratulations! You’re still stuck within a federalist system, meaning states themselves can make cannabis illegal even if federal prohibition comes to an end. And most states still outlaw marijuana for adult use.

A federal law could conceivably attempt to prohibit states from banning the drug, but that could be—and likely would be—challenged in court. Assuming more states would legalize in the absence of federal prohibition, it would still take years before most states had functioning cannabis markets.