Whether it was fear, racism or economic concerns that led the U.S. in the 1930s to ban growing or even possessing marijuana, the nation’s wall against pot lasted a generation. Now, it’s showing signs of wear.

Twenty-nine U.S. states consider pot legal for people with certain medical conditions. Eight of those states, plus the District of Columbia have legalized pot for all adults over 21.

But the United States’ marijuana experiment isn’t over. Many states still ban the drug for adults who aren’t sick, and threats to the growing industry persist because pot use remains federally illegal.

Three months into the Trump administration, on the eve of the 4/20 date celebrated by marijuana enthusiasts, here’s a look at the drug’s history in the U.S., its legal status and what’s next for the ancient but mysterious plant:

HOW WE GOT HERE

In the 1970s, at least 11 states removed criminal penalties or jail time for possessing small amounts of marijuana.

A few years later, some victims of the AIDS epidemic ravaging the U.S. began turning to pot to relieve pain, stimulate their appetites and help them sleep.

In 1996, California voters blew a hole in the anti-marijuana wall by saying sick people could use weed. The nation’s most populous state simply decided it would stop prosecuting sick people for using pot.

More than a dozen other states followed. The U.S. government expressed outrage and dispatched drug agents to the places growing and selling pot, but those sporadic raids couldn’t keep the wall intact.

Sixteen years after California voters authorized medical pot, two other Western states — Colorado and Washington — decided in 2012 that pot should be legal for all adults, not just sick people.

Within the next four years, six more states and Washington, D.C., legalized pot for adults.

WHERE ELSE IT’S LEGAL

Cannabis possession is illegal in most countries under a 1925 treaty called the International Opium Convention, and trafficking can carry the death penalty in extreme cases. Generally speaking, though, international marijuana prohibitions are thawing just as they are in the U.S.

Dozens of countries have decriminalized small amounts for personal use, with some unenforced areas of marijuana commerce, as in an Amsterdam coffee shop.

A few countries have authorized cultivation but not the sale of pot. Uruguay is the only country where it’s legal for adults who aren’t sick to grow, transport, sell and use pot. Uruguay may soon be joined by Canada, where the government has said marijuana would be made legal for recreational use by July 2018.

WHERE IT’S ILLEGAL

Actually, everywhere in the U.S., since state can’t override federal law. But enforcement of federal drug law has always relied on state and local officers, so the votes in those pot states to stop enforcing prohibition have made the federal ban essentially toothless there.

HOW HAVE U.S. AUTHORITIES RESPONDED?

Presidents from different parties have responded in similar ways to legalization measures.

Democrats and Republicans have held the White House as states defied pot prohibition. Those presidents disavowed weed — even as some admitted using it themselves as youths. Since 1996, states have seen plenty of saber-rattling from federal drug authorities but little coordinated effort to stop the pot experiments.

Not long after he was elected in 2008, President Barack Obama’s Justice Department sent an enforcement memo spelling out what states already knew: Federal authorities didn’t plan any coordinated effort to maintain blanket marijuana prohibition in states that legalized weed. In response, marijuana businesses in some states started coming out of the shadows, behaving like traditional retailers, complete with storefronts and advertising.

By 2012, when Colorado and Washington state authorized recreational pot, a few states had a fledgling marijuana industry, taxed and regulated.

So far, the federal government has kept its word about not meddling with state pot laws.

WHAT’S HAPPENING NOW?

That’s unclear. President Donald Trump said during the 2016 campaign that states should be left alone when it comes to pot. After Trump’s election, some marijuana activists thought Trump would continue Obama’s largely hands-off pot policy.

Not so fast. Trump’s spokesman and some of his Cabinet members have said marijuana legalization may not be tolerated any longer.

U.S. Attorney General Jeff Sessions said in a memo to the nation’s prosecutors this month that he’s ordered a review of existing marijuana policy to see how it may conflict with the administration’s crime-fighting agenda.

Confused? So is the industry, which continues to grow despite the uncertainty.

WHAT’S NEXT?

Several members of Congress have proposed legalizing marijuana nationwide. Similar measures have been proposed before, though, and there’s little reason to think this year’s attempt will make it to Trump’s desk. So marijuana prohibition laws are unlikely to end any time soon.

That means the Trump administration can decide how vigorously to enforce marijuana prohibition.

So far, the Justice Department and other agencies that may have a hand in marijuana enforcement have signaled more interest in tightening immigration law.

Of course, that could change at any time. The American marijuana wall may be full of holes, but it hasn’t been torn down yet.