One toke over a state line? Jeff Sessions will announce later today that the Department of Justice will end its laissez-faire approach to marijuana operations legalized at the state level. The move threatens to pit federal prosecutors against elected officials in several states where legalized pot operations have been out in the open for years:

Attorney General Jeff Sessions is going after legalized marijuana. Sessions is rescinding a policy that had let legalized marijuana flourish without federal intervention across the country.

That’s according to two people with direct knowledge of the decision. They were not allowed to publicly discuss it before an announcement expected Thursday and spoke on condition of anonymity.

The move will leave it to U.S. attorneys where pot is legal to decide whether to aggressively enforce federal marijuana law. The move likely will add to confusion about whether it’s OK to grow, buy or use marijuana in states where it’s legal, since long-standing federal law prohibits it.

In one sense, this runs counter to conservative principles about state sovereignty — but only in a very limited sense. Normally, conservatives (and certainly libertarians) would err on the side of subsidiarity, especially when production and distribution remain entirely within state lines. Given marijuana’s ubiquitous presence and the resources needed to enforce this law at the federal level, devolving the issue to the states makes sense as long as the distribution doesn’t cross state lines.

However, that itself is an issue, and so is the normal function of lawmaking under the Constitution. Federal law makes it clear that marijuana production and distribution is illegal under any circumstances, regardless of whether states like it or not. Congress can choose to amend that law or to repeal it altogether, but until Congress takes action, the DoJ has a duty to enforce federal law.

The Obama-era decisions rested on prosecutorial discretion, but that is an arbitrary basis on which to apply the rule of law, and Sessions is demonstrating its limits now. Stakeholders in these businesses, which the Associated Press makes clear include private and public entities, are about to face the risk they assumed when Barack Obama and Eric Holder unilaterally tried to change the law:

The pot business has since become a sophisticated, multimillion-dollar industry that helps fund schools, educational programs and law enforcement. Eight states and the District of Columbia have legalized marijuana for recreational use, and California’s sales alone are projected to bring in $1 billion annually in tax revenue within several years.

In other words, expect this epic battle to take place in the appellate courts more than in the marijuana crop fields of Colorado and California. States will sue to force the DoJ to back off, and who knows? Maybe a few judges will be sympathetic. However, they will be appealing to the wrong branch of government. If states want marijuana legalized, then their elected representatives on Capitol Hill should vote to change federal law first.

Whether or not the policy itself is a good idea (and that is still an open question), Sessions is at least bringing this back around to the rule of law. We need certainty and predictability in our common public life by determining as a body politic which laws we agree will be enforced on us and under what conditions rather than have a library full of laws that are only enforced by the whim of whoever is in power at the moment.  Don’t attack an Attorney General for insisting that laws be enforced properly — attack the previous administration for treating the law as its private fiefdom and Congress for its pusillanimity for avoiding this issue for the last two decades.

Update: Colorado’s Sen. Cory Gardner angrily accused Sessions of lying to him prior to his confirmation:

If Sessions misled Gardner, then he’s right to be angry about it. But if Gardner was serious about taking “all steps necessary,” why not start first with changing federal law rather than demand extrajudicial “prosecutorial discretion” to grant states the jurisdiction for these choices? He’s a member of Congress, which rumor has it can actually pass laws that control what the DoJ can and cannot do.