"Who is going to stop people from smoking pot in a residence in Denver? Federal agents?" McKay asked. "They are going to stop doing terrorism investigations and start arresting people for pot? That, to me, is crazy."

Still, a series of raids could upend the marijuana landscape and chill investment in the fledgling industry.

Financial Hurdles It's the biggest complaint in the weed business: taxes.

Businesses selling marijuana cannot use tax breaks or incentives offered to other small businesses, and some of them say they pay 80% or more of every dollar on taxes and fees. They have limited access to banking because many financial institutions are leery of the paperwork they are required to file on clients working with marijuana.

Colorado officials tried last year to ease the banking burden by setting up a special credit union to safely handle pot-shops' money, only to see the Federal Reserve Bank and federal courts block the effort.

As long as Congress and the new administration leave those hurdles in place, the marijuana business will grow haltingly. Voters may generally support pot legalization, but few have sympathy for a pot entrepreneur unable to become a multimillionaire because of banking obstacles.

Stricter Regulations Government officials who are skeptical of marijuana but also leery of going against public opinion can use regulation and red tape to slow commercial pot.

Legalization opponents frequently decry the strength of today's marijuana, an argument that provides political cover for pot skeptics who once used the drug themselves and gives legalization opponents a backdoor route to blocking weed.

In Colorado, for example, marijuana skeptics nearly succeeded earlier this year in getting state lawmakers to cap commercial pot potency. The proposal would have banned some 80% of the pot products on shelves.

Delays can be just as damaging. Even in Colorado, the first state out of the gate with recreational stores, businesses complain of long waits to get permits or licenses. A few shops were hobbled in 2015 when Denver health authorities raised alarms about pesticides, and banned the sale of thousands of plants.

In Alaska, voters legalized pot in 2014, but shops are only just now opening. Washington state spent more than a year mulling rules for the pot business.

So, What Now?

The marijuana industry has grown under three presidents, each opposed to legalized weed.

The Obama administration has generally shied away from pursuing commercial operators who comply with state-level rules. When states began pushing the marijuana experiment beyond the medical realm, former Attorney General Eric Holder urged them to keep the drug away from criminals, kids, federal lands, and other states where it remains illegal.

Marijuana activists say the pot experiment is too far along for anyone to stop, but the industry is anxious. When Sessions was announced as the attorney general nominee, the pro-legalization group Drug Policy Alliance didn't mince words.

"This was our worst nightmare," the group announced in an urgent email to supporters.