Keeping up with the laws governing marijuana use in the U.S. is a challenging ordeal these days, what with changes taking place on the state and federal level seemingly on a weekly or even daily basis, and Attorney General Jeff Sessions threatening the industry with the legal wrecking ball.

But attorney Joshua Horn is doing his best to keep on top of things. Moreover, he's sharing what he knows with the public.

"This is my passion," said Horn. "I get probably 50 news alerts a day in the cannabis space. It's just a barrage."

Horn, co-chair of the cannabis law practice and partner at the national law firm Fox Rothschild LLP, is in charge of what could be regarded as a must-have reference for anyone involved in the U.S. cannabis industry: the National Survey on Marijuana Laws and Regulations.

The 49-page survey, which can be freely downloaded at the law firm's website, offers a detailed rundown on the marijuana laws in every state and the District of Columbia, including a listing of the laws and regulations governing marijuana use in each state, any legislation that may be pending and links to related state organizations and information sources. The law firm also offers a companion reference, the Cannabis Industry State Tax Guide, that charts where every state stands in regards to marijuana taxation.

Horn checks on legal developments daily, and he updates the survey weekly -- a significant detail considering how fast states are moving to legalize marijuana for medical purposes or recreational use, or both.

Horn noted that 29 states and Washington, D.C., have already legalized medical marijuana and, with more than 90 percent of the U.S. public in support of such legalization, other states are lining up to follow.

The momentum for recreational marijuana use is also growing, he said, with nine states and Washington, D.C., already having passed such legislation.

"States want to get a better sense of what happens with their medical programs before they go recreational," said Horn, who works in Fox Rothschild's Philadelphia office.

He cited New Jersey as an example of the growing push for legalization. In past years, the state's medical marijuana laws were "eviscerated" by former Gov. Chris Christie, Horn said. But New Jersey Gov. Phil Murphy, a Democrat who took office in January, has expanded the state's medical marijuana infrastructure, setting the stage for the legalization of recreational use, Horn said.

"New Jersey will go adult use," he said.

Horn has been focused on cannabis law for four years, before that specializing in litigation in the securities industry as a lawyer for advisory firms, advisors and counselors in Finra examinations. He was inspired to get into cannabis law after taking a trip four years ago to Colorado, where he was fascinated by what he viewed as the birth of a new industry and a new field of law. "Because cannabis law was, and still is, such a new area, there is no leading treatise to rely on," Horn told the ABA Journal in a recent article. "When I set out to master it, I had to create my own curriculum."

In addition to overseeing the firm's law survey, Horn sits on the editorial board of the Cannabis Law Journal. The cannabis law practice he co-chairs encompasses about 50 attorneys at the firm, including about 15 to 20 who are actively involved in the field on a daily basis, he said.

As might be expected, much of the practice's legal work centers on helping clients -- including marijuana industry businesses and investors -- navigate a national market that is overlayed on top of 50 states that have divergent laws and regulations. What's legal in one state may be entirely illegal in another. For a national marijuana business, Horn said, that means a wrong step in just one jurisdiction could destroy an entire company.

But even with those restrictions, Horn said he continues to see unbridled growth in people investing in the industry.

"It's very robust," he said. "People are looking to put their money in the space, to deploy capital."

Not even Sessions' vow to crack down on marijuana use has slowed down the move toward legalization among states, and has perhaps even accelerated it, Horn said. One of the main reasons for this, he said, is that the marijuana businesses represent too lucrative a revenue source for state governments to ignore. Colorado, the first state to legalize weed, collected $250 million in cannabis industry tax revenues in 2017, Horn noted.

With states looking at the potential for even greater revenues, "it will be hard for the federal government to put the horse back in the barn," Horn said.

Eventually, he predicted, marijuana will take a place alongside alcohol, tobacco, gambling and cigarettes as an accepted vice that adds to states' coffers.

"People realize you can only raise taxes so high," Horn said.