In Cleveland, the Secret Service will not permit guns inside the convention hall. But delegates have been talking of bringing their personal pistols to other events. “I think it’s a very pragmatic solution,” Jamie Klein, a Pennsylvania delegate for Mr. Trump, told NPR News. “I think it’s part of Republican values, American values, to be responsible for our own safety.”

Mr. Klein, who plans to be packing his concealed 9-millimeter pistol at dinner each night, sounds all too right about Republican values. Ohio’s Republican-led Legislature, prodded by the gun lobby, has barred local governments like Cleveland from having stronger gun controls, all the while encouraging citizens to arm themselves. In Washington, the Republican-majority House of Representatives is heading off to vacation without taking up even minimalist proposals for gun safety.

“Right now, what we want to do is have a good conversation where we calm things down and we talk about solutions,” Speaker Paul Ryan explained in retreating from an issue — the ease with which terrorism suspects can buy guns — that Republicans had vowed to take up after a confessed devotee of the Islamic State last month opened fire in an Orlando nightclub, where 49 people were killed.

Mr. Ryan’s words deserve close inspection. They’re ludicrous. What he’s saying is that action urgently prompted by one gun massacre must be put off because of the distraction and grief caused by the next atrocity. This is a formula for endless procrastination in a nation where the mass shooter nightmare erupts with savage regularity.

The people vowing to swagger with their guns in Cleveland will, in a literal sense, be law-abiding. But their self-indulgence, protected by timorous politicians, can only make it easier for the next killer to obtain a military-style weapon in what amounts to an open market for mass mayhem. The Dallas shooter is reported to have obtained weapons through loopholes in the background check law that Republicans have fiercely refused to close.