“Federal law already makes it illegal for someone to possess a gun if he or she is ‘an unlawful user of, or addicted to’ marijuana or other controlled substances,” the AP reports, accurately enough. “A Sept. 21 letter from the Bureau of Alcohol, Tobacco, Firearms and Explosives, issued in response to numerous inquiries from gun dealers, clarifies that medical marijuana patients are included in that definition. ‘There are no exceptions in federal law for marijuana purportedly used for medicinal purposes, even if such use is sanctioned by state law,’ said the letter by Arthur Herbert, the ATF’s assistant director for enforcement programs and services.” Uh-oh . . .

A large number of sheriffs have signed declaration stating that they will not enforce unconstitutional federal gun regulations. A few states have passed so-called “Firearms Freedom” laws, claiming the feds have no jurisdiction over home-grown firearms (e.g. Kansas’ Second Amendment Protection Act).

When the Manchin-Toomey “expanded background checks” bill died on the Senate floor, the possibility of a state vs. federal showdown on guns decreased significantly. By the same token, the odds that a federal court will exempt a state’s firearms from the Interstate Commerce clause of the U.S. Constitution are about as high as the odds that Lisa Dergan Podsednik will be my new next door neighbor.

That said, there remains an inherent tension between states’ interpretation of gun rights and those of the federal government. You’d think this conflict would be most volatile in the gun-friendly “free states” and center on issues like “high-capacity magazines,” “assault rifles” and background checks. And you’d be right. But, once again, the inevitable confrontation could be one of those “it’s the bus you don’t see that kills you” deals.

To wit: the ATF’s decision to ban guns for residents with medical marijuana cards. It’s a potential flash point for a surprisingly large number of states. Sixteen in fact. Not to mention all the gun buyers within their boundaries.

Applying the ATF’s decision that a medical marijuana card establishes an addiction to Form 4473, if a [state] legal pot smokers ticks “yes” on the little box that asks “Are you an unlawful user of or addicted to, marijuana or any other depressant, stimulant or narcotic drug, or any other controlled substance?” they can’t buy a gun. If they tick “no” they’d be lying.

Lying on form 4473 is a federal beef. As in fines, prison and the permanent loss of gun rights. It’s also a federal crime for a drug addict to possess a firearm. Section 18 U.S.C. § 922(g)(3) of the Gun Control Act of 1968 bans firearms possession for anyone “who is an unlawful user of or addicted to any controlled substance.”

Obviously, states that have legalized or decriminalized marijuana use aren’t about arrest registered marijuana smokers for attempting to buy, own or carry a gun. Or are they? Back in 2012, Oregon sheriffs tried to rescind registered marijuana user Cynthia Willis’s concealed carry permit. The U.S. Supreme Court refused to hear the case. Leaving Willis with her guns and millions of Americans with a big problem . . .

It’s one thing for a state to forget to enforce a federal law. It’s another to decide whether or not to surrender the names and addresses of registered marijuana users to the federal government, so the feds can enter the data into the FBI’s instant background check system. Or, indeed, an ATF database.

And if the ATF feels free to categorize registered marijuana users as “addicts” what’s to stop them from labeling the 30 million or so Americans who take antidepressants addicts? Or the 10 million or so who take sleeping pills? The times may not be ripe now, but there’s no getting around the fact that massive civilian disarmament is but an ATF letter away.

This is what happens with all “gun safety” legislation: it gets abused by the people in charge of enforcing it. The camel’s body follows the camel’s nose as surely as bureaucrats seek to extend their power to justify their existence. Quite how this particular issue is going to be resolved is anyone’s guess. But one thing’s for sure: these are not the criminals the ATF is looking for. Assuming they’re looking for criminals at all.