In fact, President Trump signed a law in February revoking an Obama-era regulation that made it more difficult for the mentally ill to purchase guns.

Mr. Trump, who spoke favorably as a candidate of vigilante shootouts for self-defense, also suggested that if a civilian had not briefly exchanged shots with the Texas shooter after the massacre, the casualty toll “would have been much worse.” The implication was that the bloodshed in Texas, which also included more than 20 wounded, actually makes the case for more guns — that the disease of gun violence is also its cure.

This is a fantasy, not a rational argument; it doesn’t bear the slightest scrutiny. As our colleague Nicholas Kristof notes, the United States outstrips the world in both gun ownership per capita and gun deaths per capita. States with higher proportions of gun ownership also have rates of death by guns higher than the national average. Incidents in which victims kill attackers in self-defense are vanishingly few compared with gun homicides, and suicide is by far the leading cause of gun deaths.

From expanded background checks to assault weapons bans, proposals put forward by gun-safety proponents, unlike continually increasing private American arsenals, would do something to thwart mass shootings. The Texas killer was not motivated by racial hatred, as was the killer of the Charleston churchgoers, but by family grievance, underlining the lethal combination of domestic abuse and firearms. Abusers’ access to guns increases the risk of intimate partner homicide as much as fivefold, according to a study in the Annals of Internal Medicine. While federal law prohibits those convicted of domestic violence, as Mr. Kelley was, from buying or possessing firearms, the Air Force failed to add him to a federal database, allowing him to pass necessary background checks. The right law was on the books but enforcement was lax.

And yet so many politicians continue to promote the wares of the gun industry. Two years ago, Gov. Greg Abbott of Texas tweeted “I’m embarrassed: Texas #2 in nation for new gun purchases, behind California. Let’s pick up the pace Texans. @NRA.” On Monday he said the problem was out of human hands.

“We have evil that occurs in this world,” Governor Abbott declared, as if from a pulpit, equating all manner of global terrorist attacks, including the murder of eight last week by a truck driver in Manhattan. When asked how the evil of gun violence can be overcome, he replied “you do that by working with God.” Texas’ attorney general, Ken Paxton, even envisioned “arming some of the parishioners or the congregation so that they can respond” if another massacre occurs.

This is the level of pro-gun argument being offered by Republican leaders and some Democrats. It is made in service to the N.R.A. and the gun industry, not the American public.