The president of the International Narcotics Control Board (INCB) last Thursday voiced "grave concern" about the votes legalizing marijuana in the US states of Colorado and Washington, as well as in the Michigan cities of Detroit and Flint. INCB head Raymond Yans also warned that allowing for the legal, non-medical sale of marijuana would violate the 1961 UN Single Convention on Narcotic Drugs.

The INCB is a quasi-judicial body charged with monitoring compliance with the Single Convention and associated treaties. It hectors governments that step outside its interpretation of what the treaties allow, although in practical terms, its ability to enforce its will is mainly rhetorical. INCB criticism of Australia and Canada over the establishment of safe injection sites, for example, has not moved those governments to end the practice, nor has its criticism of Bolivia over allowing coca cultivation resulted in a shift of policy in Bolivia.

Yans was inspired to speak out by the victories of Amendment 64 in Colorado and Initiative 502 in Washington state, both of which envisage legal, state-regulated commercial marijuana cultivation and distribution regimes and both of which will result in the possession of small amounts by adults being legal by early next year. The INCB also alluded to the votes in the Michigan cities of Detroit and Flint to legalize the possession of up to an ounce by adults on private property.

"These developments are in violation of the international drug control treaties, and pose a great threat to public health and the well-being of society far beyond those states," Yans said in a statement. "Legalization of cannabis within these states would send wrong and confusing signals to youth and society in general, giving the false impression that drug abuse might be considered normal and even, most disturbingly, safe. Such a development could result in the expansion of drug abuse, especially among young people, and we must remember that all young people have a right to be protected from drug abuse and drug dependency."

This isn't your father's marijuana, Yans warned.

"Since the adoption of this Convention, very potent new forms of cannabis have appeared on the illicit market, and technological advances have been used to increase the content of the most 'active ingredient,' so to speak, in cannabis, tetrahydrocannabinol (THC). The cannabis on the illicit market today is much more dangerous than that seen in the 60s and 70s," Yans said.

Yans also noted that "for the international drug control system to function effectively, to achieve its aim of ensuring availability of drugs for medical purposes while preventing their abuse, the conventions must be universally adhered to and implemented by all states." He called on the US government "to take the necessary measures to ensure full compliance with the international drug control treaties within the entire territory of the United States, in order to protect the health and well-being of its citizens."

In the wake of last week's victories for marijuana legalization in Colorado and Washington, everyone is waiting to see how the federal government will respond. But early indications are that we may be waiting for awhile, and that the federal options are limited.

While the legal possession -- and in the case of Colorado, cultivation -- provisions of the respective initiatives will go into effect in a matter of weeks (December 6 in Washington and no later than January 5 in Colorado), officials in both states have about a year to come up with regulations for commercial cultivation, processing, and distribution. That means the federal government also has some time to craft its response, and it sounds like it's going to need it.

So far, the federal response has been muted. The White House has not commented, the Office of National Drug Control Policy has not commented, and the Department of Justice has limited its comments to observing that it will continue to enforce the federal Controlled Substances Act.

"My understanding is that Justice was completely taken aback by this and by the wide margin of passage," said Eric Sterling, former counsel to the House Judiciary Committee and currently the executive director of the Criminal Justice Policy Foundation. "They believed this would be a repeat of 2010, and they are really kind of astonished because they understand that this is a big thing politically and a complicated problem legally. People are writing memos, thinking about the relationship between federal and state law, doctrines of preemption, and what might be permitted under the UN Single Convention on Narcotic Drugs."

What is clear is that marijuana remains illegal under federal law. In theory an army of DEA agents could swoop down on every joint-smoker in Washington or pot-grower in Colorado and haul them off to federal court and thence to federal prison. But that would require either a huge shift in Justice Department resources or a huge increase in federal marijuana enforcement funding, or both, and neither seems likely. More likely is selective, exemplary enforcement aimed at commercial operations, said one former White House anti-drug official.

"There will be a mixture of enforcement and silence, and let's not forget that federal law continues to trump state law," said Robert Weiner, former spokesman for the Office of National Drug Control Policy (ONDCP). "The Justice Department will decide if and at what point they will enforce the law, that's a prosecutorial decision the department will make."

Weiner pointed to the federal response to medical marijuana dispensaries in California and other states as a guide, noting that the feds don't have to arrest everybody in order to put a chill on the industry.

"Not every clinic in California has been raided, but Justice has successfully made the point that federal law trumps," he said. "They will have to decide where to place their resources, but if violations of federal law become blatant and people are using state laws as an excuse to flaunt federal drug laws, then the feds will have no choice but to come in."

Less clear is what else, exactly, the federal government can do. While federal drug laws may "trump" state laws, it is not at all certain that they preempt them. Preemption has a precise legal meaning, signifying that federal law supersedes state law and that the conflicting state law is null and void.

"Opponents of these laws would love nothing more than to be able to preempt them, but there is not a viable legal theory to do that," said Alex Kreit, a constitutional law expert at the Thomas Jefferson School of Law in San Diego who co-authored an amicus brief on preemption in a now mooted California medical marijuana case. "Under the anti-commandeering principle, the federal government can't force a state to make something illegal. It can provide incentives to do so, but it can't outright force a state to criminalize marijuana."

An example of negative incentives used to force states to buckle under to federal demands is the battle over raising the drinking age in the 1980s and 1990s. In that case, Congress withheld federal highway funds from states that failed to raise the drinking age to 21. Now, all of them have complied.

Like Weiner, Kreit pointed to the record in California, where the federal government has gone up against the medical marijuana industry for more than 15 years now. The feds never tried to play the preemption card there, he noted.

"They know they can't force a state to criminalize a given behavior, which is why the federal government has never tried to push a preemption argument on these medical marijuana laws," he argued. "The federal government recognizes that's a losing battle. I would be surprised if they filed suit against Colorado or Washington saying their state laws are preempted. It would be purely a political maneuver, because they would know they would lose in court."

The federal government most certainly can enforce the Controlled Substances Act, Kreit said, but will be unlikely to be able to do so effectively.

"The Supreme Court said in Raich and in the Oakland Cannabis Buyers Club cases that the federal government has all the power in the world to enforce the Controlled Substances Act," Kreit said, "and if they wanted to interfere in that way, they could. They could wait for a retail business or manufacturer to apply for a license, and as soon as they do, they could prosecute them for conspiracy -- they wouldn't even have to wait for them to open -- or they could sue to enjoin them from opening," he explained.

"But you can only stop the dam from bursting for so long," Kreit continued. "In California, they were able to stop the dispensaries at the outset by suing OCBC and other dispensaries, and that was effective in part because there were so few targets, but at a certain point, once you've reached critical mass, the federal government doesn’t have the resources to shut down and prosecute everybody. It's like whack-a-mole. The feds have all the authority they could want to prosecute any dispensary or even any patients, but they haven't been effective in shutting down medical marijuana. They can interfere, but they can't close everybody down."

As with medical marijuana in California, so with legal marijuana in Colorado and Washington, Kreit said.

"My guess is that if the feds decided to prosecute in Colorado and Washington, it would go similarly," he opined. "At first, they could keep people from opening by going after them, either enjoining or prosecuting them, but that strategy only works so long."

"I think the career people in Justice will seek to block Colorado and Washington from carrying out the state regulatory regime of licensing cultivation and sales," Sterling predicted. "A lower court judge could look at Raich and conclude that interstate commerce is implicated and that the issue is thus settled, but the states could be serious about vindicating this, especially because of the potential tax revenue and even more so because of the looming fiscal cliff, where the states are looking cuts in federal spending. The states, as defenders of their power, will be very different from Angel Raich and Diane Monson in making their arguments to the court. I would not venture to guess how the Supreme Court would decide this when you have a well-argued state's 10th Amendment power being brought in a case like this."

"Enjoining state governments is unlikely to succeed," said Kreit. "Again, the federal government has taken as many different avenues as they can in trying to shut down medical marijuana, and yet, they've never argued that state laws are preempted. They know they're almost certain to lose in court. The federal government can't require states to make conduct illegal."

At ground zero, there is hope that the federal government will cooperate, not complicate things.

"We're in a wait and see mode," said Brian Vicente, executive director of Sensible Colorado and co-director of the Amendment 64 campaign. "It's our hope that the federal government will work with Colorado to implement this new regulatory structure with adequate safeguards that make them comfortable the law will be followed."

While that may seem unlikely to most observers, there is a "decent chance" that could happen, Vicente said. "Two mainstream states have overturned marijuana prohibition," he said. "The federal government can read the polls as well as we can. I think they realize public opinion has shifted and it may be time to allow different policies to develop at the state level."

The feds have time to come to a reasonable position, said Ethan Nadelmann, executive director of the Drug Policy Alliance.

"There is no need for a knee-jerk federal response, since the states are not required to create a regulatory scheme quickly," he said. "And while anti-marijuana forces more or less captured the drug czar's office early in Obama's first term, they're at odds with other people in the White House and the Obama administration whose views may be closer to our own. I think the White House will be the key. It's very likely that the fact that Attorney General Holder said nothing about the initiatives this fall, unlike two years ago, was because of the White House. I don't mean the drug czar's office; I mean the people who operate with respect to national politics and public policy."

Sterling disagreed about who is running drug policy in the Obama administration, but agreed that the feds have the chance to do the right thing.

"Given the large indifference to drugs as an issue by the Obama administration, its studious neglect of the issue, its toleration of an insipid director of ONDCP, its uncreative appointment of Bush's DEA administrator, it's clear that nobody of any seniority in the Obama White House is given this any attention. Unless Sasha and Malia come home from school and begin talking about this, it won't be on the presidential agenda, which means it will be driven by career bureaucrats in the DEA and DOJ," he argued.

That's too bad, he suggested, because the issue is an opportunity for bold action.

"They should respond in a vein of realism, which is that this is the future, the future is now," he advised. "They have an opportunity with these two different approaches to work with the states, letting them go forward in some way to see how they work and providing guidance in the establishment of regulations that would let the states do this and ideally minimize the interstate spillover of cultivation and sales."

"As part of that, they should ideally move to rewrite the Controlled Substances Act and begin working in the UN with other countries to revise the Single Convention on Narcotics. Our 100-year-old approach is now being rejected, not simply by the behavior of drug users, but by the voters, many of whom are not drug users," Sterling said. "That would be a way that a wise, forward-thinking, statesman-like public official should respond."

That would indeed be forward-thinking, but is probably more than can be reasonably expected from the Obama White House. Still, the administration has the opportunity to not pick a fight with little political upside, and it has time to decide what to do before the sky falls. Marijuana legalization has already happened in two states, and is an increasingly popular position. The federal government clearly hasn't been in the lead and it's not going to be able to effectively stop it; now, if it's not ready to follow, it can least get out of the way.