This weekend brings appalling news that a failure in the background check process led Columbia shooter Dylann Roof to make a gun purchase that should have been prevented and flagged as illegal:

Dylann Roof, who is accused of killing nine people at a church in South Carolina three weeks ago, was able to purchase the gun used in the attack only because of lapses in the FBI’s background-check system, FBI Director James B. Comey said Friday…

The breakdown was a result of errors not only by the FBI but also apparently by local law enforcement, and Comey said he has ordered a 30-day review to examine the procedures that led to the failure and to see if the process can be tightened. The errors came to light as investigators examined a gun purchase Roof made two months before the shooting.

Roof had been arrested for possession of narcotics in February, a felony charge that alone did not disqualify him from buying a gun. But Comey said Roof’s subsequent admission of the drug crime would have triggered an automatic rejection of his gun purchase if the information had been properly recorded in criminal-record and background-check databases.

Part of the problem was a breakdown in communication and control between federal and local law enforcement–a problem that could easily by fixed by requiring federal reporting of all gun sales. That, of course, is something that conservative legislators refuse to allow.

On a broader level, though, it’s instructive that the United States spends trillions of dollars on wars overseas, on a massive Department of Homeland Security and on mass surveillance of questionable legality at the NSA, all ostensibly to prevent terrorist attacks and to keep Americans safe.

But the greatest violent threat to our safety comes not in the form of Islamists with bombs, but from domestic extremists with guns. And to this day, supposedly national security-minded Republicans refuse to even make the slightest effort to keep Americans safe by doing more to keep guns out of the hands of criminals and domestic extremists–even though violence by right-wing domestic extremists has surpassed that of Islamists since 9/11.

The most important action Americans can take to stop the terrorism that puts us most in danger is to toughen gun laws and background checks. Not to torture people, not to engage in mass surveillance, not to bomb countries overseas. Even among Islamist terrorists, the greatest danger comes from lone wolves inspired by ISIS who are unlikely to get their hands on anything more deadly than a conventional firearm. But that is plenty deadly enough.

It’s time to do something about it.

David Atkins

Follow David on Twitter @DavidOAtkins. David Atkins is a writer, activist and research professional living in Santa Barbara. He is a contributor to the Washington Monthly's Political Animal and president of The Pollux Group, a qualitative research firm.