While political power has been shifting to the federal level lately, there's a clear exception. When it comes to policies on marijuana for medicinal use, the Obama administration has declared that states can decide for themselves.

Federal law prohibits marijuana possession, even for medicinal purposes. Some 13 states have gone ahead and permitted medical marijuana anyway, flouting the federal law and creating some legal ambiguity over the issue. Last year, the U.S. Justice Department cleared up the matter by announcing that medical marijuana won't be a focus of federal law enforcement in those states. That opens the door for even more states to allow marijuana use for medicinal purposes and may encourage a few states to reach even further.

Most current state laws allowing medical marijuana are the product of ballot measures, not legislative action. So one question for 2010 is whether legislatures will take up the cause. The first test wasn't promising for advocates: Lawmakers in New Hampshire fell just short of overriding Governor John Lynch's veto of a medical-marijuana bill late last year. Key votes could come soon in Illinois and New York, with law enforcement officials leading opposition to the proposals.

Some states are likely to go beyond the question of legalizing medical-marijuana use. Allowing retail sales of pot for medical purposes would be the next step. Only five states currently permit such sales; in the other eight states where medical marijuana is legal, users have to grow it themselves or have a caregiver give it to them for free. With the new federal policy, however, more states may decide that if they're going to allow people to smoke pot for medical reasons, they might as well allow it to be bought and sold for those reasons, too.

A few states, including California and Rhode Island, will consider something that the Obama administration has shown no inclination to tolerate: marijuana possession for recreational purposes. "This sort of reform is not going to start from the federal level," says Bruce Mirken, a spokesman for the Marijuana Policy Project, an organization that lobbies for looser marijuana laws. "It's going to start with the states, and the feds are going to be dragged kicking and screaming."