Marijuana prohibition advocates are giddy at the news Friday that President-elect Donald Trump will nominate Sen. Jeff Sessions to be his administration’s first attorney general.

The Alabama Republican is one of the nation’s most consistent and quotable foes of pot legalization, and at the helm of the Justice Department he could aggressively enforce federal laws that criminalize possession of pot for any reason outside limited research.

Sessions has condemned President Barack Obama for saying marijuana is less dangerous than alcohol and for taking a hands-off approach that allowed states to regulate recreational pot markets following passage of 2012 ballot initiatives.

At an April hearing, Sessions predicted support for state-level legalization would “ripple throughout the entire American citizenry” and said: “We need grown-ups in charge in Washington to say marijuana is not the kind of thing that ought to be legalized, it ought not to be minimized, that it is in fact a very real danger.”

At the hearing he praised the “Just Say No” anti-drug campaign of former first lady Nancy Reagan and expressed concern about the undoing of years of effort “trying to send that message with clarity that good people don’t smoke marijuana.”

As attorney general, Sessions could withdraw a 2013 policy document called the Cole Memo that gave states a green light to unfurl retail pot businesses. Or he could intensely scrutinize compliance with priorities the memo said could trigger federal intervention, including interstate smuggling, increases in drugged driving or health consequences.

The Obama administration has allowed states broad autonomy to set their own marijuana policies independent of federal law, with residents of eight states and the nation's capital voting to allow recreational use, and more than half of states adopting medical use laws.

A multibillion-dollar industry has been built on non-enforcement of federal prohibition. Although states likely could not be forced to recriminalize or enforce federal laws against personal possession, federal intervention could shutter regulated businesses.

Ethan Nadelmann, executive director of the large pro-legalization Drug Policy Alliance, calls Sessions a “drug war dinosaur” and tells U.S. News the group will stridently encourage Sessions’ colleagues in the Senate to vote down his nomination.

“There definitely will be a major campaign to block Sen. Sessions’ nomination,” he says. “Sessions’ nomination represents a disaster for all we fought for.”

Emerging marijuana businesses frequently are criticized by policy organizations for not reinvesting enough in the movement to make or keep marijuana legal. Nadelmann says with an aura of inevitability too many people have assumed there’s no threat to the industry, but he says business owners should now donate and lobby as though their freedom and livelihoods depend upon it.

“The marijuana industry is such a new and young industry that they have yet to achieve all that much political sophistication and they have not shown themselves as yet at being effective at organizing to influence national policy,” Nadelmann says. “But the nomination of Sessions is undoubtedly the wakeup call they needed.”

Kevin Sabet, a former presidential drug policy adviser who leads the national anti-legalization group Smart Approaches to Marijuana, agrees with Nadelmann that Sessions’ nomination is dire news for legalization.

“Well, let's just say that if I had marijuana stocks right now, I'd be shorting them,” he says. “This is a man who we know is staunchly anti legalization. There's no way around that. Things are about to get interesting. I'd think marijuana investors -- and legalizers -- might be rethinking their strategy right now.”

Sessions’s colorful denunciation of marijuana has spanned the years. In 2014 he pointed to Lady Gaga’s claim of addiction to marijuana as evidence “it is not harmless” and separately scolded FBI Director James Comey for suggesting the government could hire a more talented workforce without a three-year ban on pre-employment pot use.

“Do you understand that that could be interpreted as one more example of leadership in America dismissing the seriousness of marijuana use?” Sessions told Comey.

During a confirmation hearing for current Attorney General Loretta Lynch in 2015, Sessions used his speaking time to extract a statement from Lynch that she does not support marijuana legalization.

The threat to the industry is well-understood. Before the pick of Sessions, reformers expressed concern about two other Trump allies seen as contenders for the post, former New York City Mayor Rudy Giuliani and Gov. Chris Christie, R-N.J.

"This entire industry in Colorado and Washington and places like that is all built on a policy memo from the Department of Justice, and policy memos can be pulled back by the next attorney general, no question," Tim Purdon, a former U.S. attorney for North Dakota, told U.S. News last week.

But concern about Sessions has not reached a panic level among all legalization backers, some of whom seem to have accepted that he is likely to be confirmed.

Aaron Smith, executive director of the National Cannabis Industry Association, released a short statement, framing the issue in terms that might appeal to Sessions: "Voters in 28 states have chosen programs that shift cannabis from the criminal market to highly regulated, tax-paying businesses. Senator Sessions has long advocated for state sovereignty, and we look forward to working with him to ensure that states' rights and voter choices on cannabis are respected."

Tom Angell, chairman of the pro-legalization Marijuana Majority, said Trump’s campaign-trail support for state autonomy on marijuana policy, along with majority support for legalization in national polls, also are safeguards for the industry.

“During the campaign the president-elect clearly pledged to respect state marijuana laws, and he should keep his word -- both because it’s the right thing to do and because a reversal would be a huge political misstep,” Angell said.

Mason Tvert, a spokesman for the Marijuana Policy Project, a national group that's been influential passing ballot initiatives, also pointed to Trump's position, saying it would be highly controversial if Sessions went after state marijuana laws.

"There is a large and growing sentiment in Congress and among the American public that our federal government should not be wasting tax dollars enforcing failed marijuana prohibition laws," Tvert says. "We hope Sen. Sessions or whoever is confirmed as our next attorney general will use federal law enforcement resources to protect our country's citizens, not to defy the laws those citizens have adopted."

If Sessions becomes attorney general, there's reason to believe he won't have carte blanche to take a wrecking ball to cannabis markets, even in a worst-case scenario for reformers. Though Trump has said he personally opposes legalization of marijuana for recreational use, he also has said he supports legal access to medical marijuana, which has about 90 percent support in polls and presently is protected by a budget rider.