• A more straightforward way to legalize marijuana would be for Congress to pass a law, though even if that happened, states that wanted to outlaw marijuana could do so.

• An executive order would start a regulatory process that could take months or years, with no guarantee of success.

• Berrnie Sanders has said on multiple occasions that he would legalize marijuana nationally soon after taking office through an executive order. But it’s not that easy.

One of Bernie Sanders’ biggest applause lines on the campaign trail has been his proposal to legalize marijuana — something that is illegal under federal law, despite the decision by 11 states and the District of Columbia to legalize marijuana for recreational use, and dozens of other states for medical purposes.

At times, Sanders has made a bold claim — that if he’s elected president, he can legalize marijuana nationwide by executive order, a process that sidesteps Congress and the full regulatory process

"On my first day in office, through executive order, we will legalize marijuana in every state in this country," Sanders said at a rally before the Iowa caucuses. He’s also tweeted that, "as president, I will immediately issue an executive order to declassify marijuana as a controlled substance." And he touted this approach in an interview with radio host Joe Rogan.

How realistic is the idea of legalizing marijuana by executive order — a single memo from the president’s desk? Legal experts said Sanders has several avenues for moving toward legalizing recreational marijuana, but they doubt that he could do it quickly or easily.

Indeed, the marijuana issues page on Sanders’ website uses the term "executive order" only once, when it says that Sanders would order the attorney general to start the regulatory process of making marijuana legal. But that wouldn’t accomplish legalization by itself; that would kick off a months- or years-long process, with no guarantee of success. Mostly, the website uses the term "executive action," a less-specific term.

Let’s take a look at how the process would work.

What’s the current legal status of marijuana?

What’s preventing the national legalization of marijuana is a longstanding law called the Controlled Substances Act.

The law has long defined marijuana as a "Schedule I" substance, meaning that marijuana has a high potential for abuse and no current accepted medical use. Marijuana advocates disagree with that assessment, and they urge "rescheduling" marijunana to a lower level that imposes fewer restraints on its use.

The most straightforward way to do this would be to pass a new law updating the Controlled Substances Act. Bills to do this have been proposed for decades, but so far to no avail.

An alternative method that bypasses Congress would be to use the federal regulatory process. Here’s how that would work, according to Brookings Institution scholar John Hudak.

After an official request, the secretary of Health and Human Services would open a scientific and medical evaluation by the Food and Drug Administration to determine whether marijuana’s scheduling status should be changed. The last time FDA reaffirmed marijuana’s Schedule I status was in 2006.

Meanwhile, the attorney general, most likely through the Drug Enforcement Administration, would open a parallel review. As recently as 2011 — during the relatively marijuana-tolerant Obama administration — the DEA reaffirmed that marijuana has no accepted medical use.

If these agencies were to reverse course and recommend downgrading marijuana’s scheduling, a regular rule-making process governed by the Administrative Procedures Act would begin. The White House’s Office of Management and Budget would also weigh in with its own review.

It’s not clear exactly how long this process could take, but it would not be quick.

"It’s true that a President Sanders could direct one of these officers to initiate such a process, but it’s hardly a day-one, first-hour thing," Sam Kamin, a professor of marijuana law and policy at the University of Denver, told PolitiFact.

Other obstacles

Hudak and other experts noted some additional challenges to rescheduling marijuana.

One, Hudak writes, is that if cannabis came under the control of FDA as a prescription drug, it would be subject to "tremendous testing and myriad regulatory requirements that are far beyond what states currently implement. That outcome may not be what legalization advocates would want in the end."

Another issue, he writes, are international treaties that include the United States. Reconciling mismatches between U.S. treaty obligations and the new U.S. policy would likely require cooperation from the World Health Organization and the United Nations.

A third concern is that states can decide to keep marijuana illegal even if the Controlled Substances Act no longer considers marijuana part of Schedule I.

"The states can’t be forced to change their laws just because the president says so," Kamin said. "That was true when the states were legalizing, and those in Washington wanted to stop them. It’s equally true of those states that will want to keep their marijuana prohibitions in place."

A pro-legalization presidential administration may be able to leverage state cooperation on legalization through the federal budget — the federal government has previously leveraged highway funding to get states to raise the drinking age to 21 — but states would be within their rights to keep their anti-marijuana laws on the books.

Doubts about an executive order

These obstacles would be even larger if a president tried to accomplish the task by executive order, rather than by the well-trodden paths of congressional legislation or regulatory action, experts said.

Hudak of Brookings told the publication Marijuana Moment that executive orders require authority from either the Constitution or a federal law to make a policy change. That’s a problem, he said, because the president is explicitly restricted by the Controlled Substances Act from doing it through a non-regulatory process.

"It’s not feasible to legalize marijuana nationally by executive order," said University of Michigan law professor Julian Davis Mortenson. "An executive order can’t repeal the state laws prohibiting marijuana, and it can’t repeal federal criminal law."

Meanwhile, any presidential effort to pardon all marijuana crimes would be limited to federal crimes. A president could not pardon state offenders, who comprise the bulk of marijuana convictions. Sanders’ campaign says he understands this and would seek to encourage states to set up their own systems for providing relief to those with past marijuana convictions, as California has done.

Possible options for a President Sanders

So what could a President Sanders do to advance his marijuana priorities?

He could try to push Congress to pass a new law. Given the growing support for legal marijuana — two-thirds of Americans now support it, according to Gallup — this is a lot more plausible than it was even a few years ago.

He could try the regulatory route, although — like congressional action — it could take a while.

Or Sanders could decline to enforce federal laws on marijuana. "That’s not nothing," Mortenson said. But he added that it would raise constitutional issues similar to those that have caused judicial questioning of President Barack Obama’s Deferred Action for Childhood Arrivals policy. That policy paused prosecutions of undocumented immigrants who arrived in the United States while they were children.

Josh Orton, the Sanders’ campaign’s national policy director, said Sanders is committed to trying several of these approaches.

He "sees the racist war on drugs and mass incarceration as an ongoing crisis, and as something that needs to be reversed as quickly as possible," Orton said. "As president, he will pursue every avenue possible."