Attorney General Jeff Sessions’ announcement that the federal government will prosecute possession and sale of marijuana in states where it is legal is stunning conservative hypocrisy.

Throughout American history, conservatives have championed “states’ rights.” Sessions himself has done so on countless occasions, such as when he rescinded the Obama administration policy interpreting federal law to protect transgender students. But when Sessions does not like what states are doing, such as legalizing possession of small amounts of marijuana, his commitment to federalism and states’ rights vanishes.

In 2013, the Justice Department issued the “Cole memo,” which said that the federal government would not enforce the Controlled Substance Act’s ban on marijuana in states that had legalized it. In this way, the federal government announced that it would let these states deal with marijuana as long as they did not threaten other federal priorities, such as preventing the distribution of the drug to minors and targeting cartels.

The Cole memo allowed local marijuana sellers to be confident that they wouldn’t be prosecuted if licensed by a state. On Jan. 5, Sessions said that he was rescinding the Cole memo and returning to the “rule of law.”

Twenty-nine states, including California and Maine, have approved the sale of marijuana for medical purposes. Eight states – Alaska, California, Colorado, Maine, Massachusetts, Nevada, Oregon and Washington – also have legalized sale and possession of small amounts of recreational marijuana. Sessions’ announcement undoubtedly was in response to the California law legalizing recreational marijuana, which took effect Jan. 1. The federal policy shift creates great uncertainty for businesses that sell and distribute marijuana.

The federal government clearly has the legal authority to prosecute and punish sale or possession of marijuana under current law. Marijuana remains a Schedule 1 controlled substance under the federal Controlled Substances Act, along with opioids like heroin, and hallucinogenics like LSD.

A state’s choice to legalize marijuana, for medical or recreational use, means that the state government will not prosecute sale or possession. But that cannot keep the federal government from doing so.

A state can have any law it wants with regard to marijuana. A state may choose to have no ban on marijuana, or a ban with an exception for medical use, or a law allowing possession of small amounts of the drug, or anything else it wants.

But a state’s choice to legalize marijuana has no effect on the federal law or federal enforcement of it. Under current law, possession of marijuana is still a federal crime and the federal government can choose to enforce its law however it chooses. Legalization by a state, in some or all circumstances, just means that it is not a state crime.

Contrary to what many believe, marijuana laws continue to be enforced. According to FBI statistics, 693,482 individuals in the United States were arrested in 2013 and charged with marijuana violations, and of these, 609,423, or 88 percent, were arrested for simple possession.

There is an enormous cost in terms of law enforcement resources, the criminal justice system and people’s lives for marijuana to remain illegal. Even for those arrested and never prosecuted or convicted, arrest records have real harms in terms of the ability to get jobs, loans, housing and benefits.

Like all drug laws, the prohibition against marijuana is much more likely to be enforced against African-Americans and Latinos than against whites. According to a 2013 study, whites and blacks use marijuana at roughly the same rates, but blacks are 3.7 times more likely than whites to be arrested for possession of marijuana.

Yet, there is little benefit of illegality. The primary argument for keeping marijuana illegal is that it is harmful. But as then-President Barack Obama observed, pot is not “more dangerous than alcohol.” Many things are harmful – cigarettes, foods high in sugar and salt and cholesterol – but that does not mean that they should be illegal.

In fact, there is a good deal of evidence that marijuana is significantly less harmful than tobacco or alcohol and that it has benefits in treating some medical conditions, such as glaucoma and seizure disorders, and alleviating some of the ill effects of chemotherapy.

Ultimately, though, the question is whether states should be able to decide this question for themselves, including choosing to gain the taxes from legal marijuana. One would expect that a conservative president and attorney general would think so.