THE TIME of mourning for the victims of mass shootings in America, including those a week ago in El Paso and Dayton, Ohio, may never end. The time for policymaking action, though, has definitely arrived. It is long overdue.

The United States faces a grave threat to public safety. The Post reports that mass shootings took place roughly twice a year between 1966 and the massacre at Columbine High School in Littleton, Colo., in 1999. Between Columbine and the slaughter at a predominantly African American church in Charleston, S.C., in June 2015, the pace was roughly five times a year. Since the white-supremacist attack in Charleston, there’s been one almost every six weeks. And these data reflect a restrictive definition of mass shootings: those that claimed at least four lives, not including perpetrators, in public places or large private gatherings.’s broader definition, which encompasses a wider-range of multiple-victim shootings, fatal and nonfatal — including those tied to such crimes as robbery and domestic abuse — produces 254 just this year, through last Wednesday.

It is a measure of public outrage at this situation that President Trump and Senate Majority Leader Mitch McConnell (R-Ky.) now feel politically constrained to mouth interest in Senate consideration of federal gun laws of the kind they have opposed or allowed to fail in the past. Mr. Trump says he supports “very meaningful background checks.” Mr. McConnell says such a proposal could be “front and center” at the Senate in September. Yet the president threatened to veto a bill providing for background checks on private gun sales when the House passed it in February; Mr. McConnell froze it out of the upper chamber. If the National Rifle Association’s hammerlock on GOP politics has loosened, maybe the results will be different now. We’ll believe it when we see it.

Background checks and so-called red-flag laws, the subject of another bill backed by Sens. Lindsey O. Graham (R-S.C.) and Richard Blumenthal (D-Conn.), represent only the bare minimum of reform. To tackle the specific, acute problem of mass public shootings, Congress must address the actual hardware: assault-style firearms, along with large-capacity magazines. Both should be banned, as assault weapons were at the federal level between 1994 and 2004, and as the law in several states already provides.

If anything, the large-capacity magazine ban may be the highest priority: Such devices, which augment the lethality of semiautomatic weapons, were involved in half of the 62 mass shootings between 1982 and 2012, according to a 2013 report for Mother Jones. A 100-round drum of bullets enabled the Dayton shooter to fire 41 shots in less than 30 seconds. “It is fundamentally problematic,” the city’s police chief observed, “to have that level of weaponry in a civilian environment, unregulated.” Could the president or Mr. McConnell look him in the eye and deny it?

In emphasizing measures to stop mass public shootings, we do not forget that the vast majority of gun-related death occurs in — alas — more ordinary contexts. Suicide, street crime and domestic violence are chronic problems, and they also cry out for intelligent response. But what we must refer to as “conventional” homicide has waned even as mass public shootings have increased. Swift action aimed specifically at this socially destabilizing phenomenon is a must, lest our public spaces become places of permanent latent anxiety, subject to random lethal attack — or, as occurred in Times Square the other day, panicked stampedes at the sound of a motorcycle backfire.

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