I’m already seeing some lefties refer to this as a “loophole” in the background check system, falsely suggesting that a flaw in the law itself made Roof’s purchase a legal one. And by “some lefties,” I mean the New York Times.

There was no “loophole.” There was a mistake.

The FBI began a background check, but a federal examiner didn’t obtain a report on a Columbia, S.C., arrest record from March 1 that showed he had admitted to using drugs. That should have disqualified him from buying a firearm. But Mr. Comey described a complicated city and county jurisdictional arrangement in the Columbia area that made it difficult for the FBI examiner to unearth the record…

Mr. Comey said the FBI examiner ran numerous checks but didn’t see that Mr. Roof had admitted being an “unlawful user” of drugs as part of his recent arrest. His case was pending in South Carolina court, however, making it more difficult to find a concrete report.

“She’s obviously heartbroken and struggling, as you might imagine,” Mr. Comey said.

Being charged with felony drug possession doesn’t automatically bar you from buying a gun unless you admit to it, as Roof did. Somehow the examiner missed that notation and approved the purchase. Comey himself is describing this to families of the victims as a “mistake” that shouldn’t have happened. “We [gun-rights advocates] don’t chafe at the notion of new gun laws because we want bad people to have guns or because we enjoy gun violence,” writes Sean Davis. “We chafe at them because time and time again, like in Charleston, they completely fail to prevent bad people from getting their hands on guns.” The unsolvable counterfactual is what Roof would have done if his purchase had been blocked. Would he have given up on his plot, would he have stolen a gun a la Adam Lanza and carried it out, or would he have resorted to some other mode of terrorism, like arson or setting off bombs? A guy capable of writing this sounds like he wouldn’t be so easily deterred.

Another fascinating question being kicked around by more libertarian-minded gun-rights activists on Twitter: Should someone charged with drug possession be barred from buying guns as a rule? Should someone convicted of possession? What if they have no record of violence? What if the drug they were busted for isn’t typically associated with violent behavior, e.g., marijuana? An alcoholic with a gun may well be more dangerous than a pothead with one. Why not screen for alcohol consumption as part of the check?