Sessions’s memo opens up an interesting rift between antidrug Republicans and states’-rights Republicans. “Jeff Sessions has forgotten about the Constitution and the Tenth Amendment,” said Representative Dana Rohrabacher, a Republican from California and sponsor of the amendment, on a call with reporters.

“People see the impact of this stupid mindset from the 1950s and early ’60s,” he later added. “That’s what Jeff is representing, I’m afraid.”

If the Rohrabacher-Blumenauer amendment goes away, federal agents could start raiding and shutting down medical-marijuana dispensaries with renewed vigor.

Under the Bush administration, DEA agents shut down 30 to 40 medical dispensaries, sometimes raiding them even if they appeared to be lawful. Eric Holder, the attorney general under most of President Obama’s tenure, signaled he would end law-enforcement raids on legitimate medical dispensaries in 2009. Still, medical-marijuana dispensaries in New Mexico, California, Colorado, and elsewhere were being raided throughout the Obama administration, sometimes for allegedly violating rules that came with the Obama administration’s supposedly more lenient approach, like trafficking marijuana outside state lines.

“There’s no question that Obama’s the worst president on medical marijuana,” Rob Kampia, then the executive director of the Marijuana Policy Project, told Rolling Stone in 2012.

But now, 60 percent of states have a medical-marijuana program, so the pressure might be on Congress to renew the amendment. Medical marijuana is more popular than the recreational kind since some find it helps PTSD, epilepsy, and other ailments. “It’s harder for a politician to say, ‘you wounded Iraq veteran, go ahead and suffer, because we want to shut down your program,’” said Franklin Snyder, a professor of law at Texas A&M University. “It’s much easier to say, ‘you Colorado hippie potheads, we don’t want you smoking dope to get high.’”

On the call, Rohrabacher suggested that the move by Sessions would “mobilize people” and that he hopes to get a law passed that says “the federal government will respect all of the decisions of the states when it comes to cannabis.” He also said he plans to hold the president’s “feet to the fire,” since on the campaign trail Trump seemed rather neutral on marijuana.

Doug Berman, a professor of law at Ohio State University, thinks the policy change might not end up being that radical, especially if it mainly targets “bad players”—dispensary owners who don’t follow regulations. Even so, “an effort even to take a scalpel to the industry might nick the more responsible players.”

Mark Kleiman, a professor of public policy at New York University, says “the most likely practical consequence of this decision is to drive young voters to the polls this November.”

Either way, this adds to the chilling effect for an industry that already faces strict regulations and an awkward dance between state permissiveness and federal prohibition.

Would-be dispensary owners might think, Berman said, “Wow, another headache, another hurdle, another layer of uncertainty. I shouldn’t bother putting my money in this.”