William Britt, left, and Al Moreno celebrate after Californians voted to pass Prop 64, legalizing recreational use of marijuana in their state, in Los Angeles. (Jonathan Alcorn/Reuters)

Americans wake up this morning to find a drug policy landscape radically altered from yesterday. California, Massachusetts and Nevada have legalized recreational marijuana, while voters in a handful of Southern and deeply conservative states embraced medical marijuana with open arms.

Regardless of how a still-contested legalization vote turns out in Maine, more than 1 in 5 Americans now live in states where the recreational use of marijuana is, or soon will be, legal.

“This is the most momentous Election Day in history for the movement to end marijuana prohibition,” Rob Kampia of the Marijuana Policy Project, a group that supported a number of the legalization initiatives, said in a statement. “The end of prohibition is near, and it would be a mistake for the federal government to continue waging war on its own nonviolent citizens. How do you ask a DEA agent to be the last man to enforce a mistake?”

But jubilation over marijuana's ballot wins was quickly tempered by the uncertain future marijuana faces under a Trump Justice Department. “The prospect of Donald Trump as our next president concerns me deeply,” Ethan Nadelmann, executive director of the Drug Policy Alliance, said in a statement. “His most likely appointees to senior law enforcement positions — Rudy Giuliani and Chris Christie — are no friends of marijuana reform, nor is his vice president.”

Regardless of what happens at the state level, marijuana remains illegal for all uses under federal law. The Obama administration has officially adopted a policy of noninterference with state marijuana laws, as outlined in a 2013 memo by then-Deputy Attorney General James Cole.

In the Cole memo, the Justice Department acknowledged the reality that most drug enforcement is carried out by state and local — not federal — authorities. The department's position has been that as long as state legalization efforts didn't threaten certain federal priorities — like keeping marijuana out of the hands of minors, preventing driving while under the influence of drugs and keeping marijuana grow operations out of federal lands — it would exercise “prosecutorial discretion” and direct its limited law enforcement resources to other drug priorities, such as dealing with the opiate epidemic.

Voters in California, Maine, Massachusetts and Nevada just approved recreational marijuana use. Here's what they can learn from Washington, Colorado and Oregon, states where marijuana use has already been legalized. (Daron Taylor,Danielle Kunitz/The Washington Post)

John Hudak, a senior fellow at the Brookings Institution who studies marijuana policy, said this memo was instrumental in allowing Colorado and Washington to set up their recreational marijuana markets. “A lot of people forget that [recreational marijuana markets in] Colorado and Washington were pretty much on hold until the governors there received guidance from the Department of Justice,” Hudak said in an interview.

The Drug Policy Alliance's Nadelmann agrees. “I don't think we're going to have quite the same green light coming out of the new administration,” he said in a conference call with reporters.

Reversing the Obama administration's hands-off approach to marijuana would be as simple as withdrawing the Cole memo, Hudak says. And if that were to happen, it's unclear what the effect would be both in states that already have recreational marijuana and in places where state governments are setting up marijuana markets after this year's ballot measures.

“It could have a chilling effect on the willingness of states to move forward with the creation of these systems,” Hudak said. “It could also have a pretty chilling effect on investment in marijuana businesses.”

But some congressional observers are skeptical that there will be any appetite in a new Trump administration for quashing marijuana reform. "Go against millions of supporters, against states' rights, against where the public is?" said Rep. Earl Blumenauer (D.-Ore.) in an interview. "It would be the beginning of tremendous problems for the Trump administration that they don't need."

Blumenauer remains optimistic that Congress will tackle a number of issues that have been vexing marijuana businesses in recent years, including their lack of access to the federal banking system and their inability to take the same tax breaks that other businesses are entitled to.

"The number of men and women in Congress who are now going to represent state legal businesses [will see] a quantum increase" as a result of the legalization of recreational marijuana in California, and the creation of a medical market in Florida, Blumenauer said.

Opponents of legalization, meanwhile, are regrouping and considering how to address the new reality they face in the coming months and years. Smart Approaches to Marijuana, the nation's leading anti-legalization group, announced yesterday an initiative aimed at reform and oversight of the existing marijuana industry.

The group's founder and executive director, Kevin Sabet, said in an email that this in no way represents a shift away from trying to stop legalization from happening. “We still plan to stop legalization,” he said, pointing to the group's successful effort to oppose the marijuana legalization measure in Arizona as a blueprint.

“I am feeling (strangely, maybe) optimistic,” Sabet added. “We won in Arizona. The overarching lesson was that if we could raise enough money early, we can win. Arizona was the only state where we were toe to toe with the 'yes' side, and it's the only state we started early in.”

On marijuana, as on so many issues, Trump is something of a wild card. He has surrounded himself with tough law-and-order advisers, including former New York mayor Rudy Giuliani and New Jersey Gov. Chris Christie (R).

Trump's own statements don't offer much clarity on the topic. He has been vociferous about the negative effects of legalization but also said that recreational and medical marijuana should be treated at the state level.

Beau Kilmer, a drug policy expert at the nonprofit Rand Corp., said it's unlikely that any sort of changes to marijuana law will be a priority for incoming Trump administration officials. “In the grand scheme of top issues the new administration is going to be dealing with, marijuana is not going to be a top priority,” Kilmer said in an interview.

With 65 million people living in states that have given the green light to marijuana legalization, any federal crackdown “could have significant political costs associated with it,” Kilmer said. And the burgeoning marijuana industry is likely to step up its lobbying efforts at the state and local levels.

Hudak agrees that any effort to stop state-level legalization will depend on lawmakers' appetite for dealing with the potential political fallout from the move.

“This is a Congress that is about to repeal the Affordable Care Act,” Hudak said. “I think a Congress and an administration that are willing to do that are not going to worry about the optics of quashing the marijuana industry.”