Many in Britain took great exception to President Donald Trump’s comments about the rash of knife attacks and murders that have plagued London in recent months. Speaking to the National Rifle Association’s annual convention last week, Trump called back to an old NRA talking point when, after noting Britain’s “unbelievably tough gun laws,” he added: “They don’t have guns, they have knives and instead there’s blood all over the floors of this hospital. They say it’s as bad as a military war zone hospital.”

You might guess the NRA slogan behind Trump’s inference — that “guns don’t kill people, people kill people.” The broader context of the president’s comment is not only that killings in London have spiked, but also that for the first time in anyone’s memory, London’s murder rate exceeds that of New York City: In March, 22 people were killed with knives and guns in London, compared with New York’s 21. This caps a three-year, 40 percent rise in London killings compared with an 87 percent drop in murder in the Big Apple dating to 1990.

Many factors have been cited for this dismaying trend, including the failure of British courts to more effectively enforce its “two strikes” law, which calls for mandatory prison for those caught twice carrying a knife. London has also witnessed an upsurge of gang- and drug-related violence.

So the NRA’s reaction was predictable: “Having stripped the law-abiding of the most useful means of self-defense [i.e. guns], activists and government officials now busy themselves with knife control.”

Despite the inference that the substitution of knives for guns yields the same result in human destruction, though, one thing Trump doesn’t know — and the NRA will not admit — is that this is not true.

As criminologists and medical professionals know, the weapon used to inflict harm on a human being matters — a great deal. The “weapon instrumentality effect” refers to the well-understood fact that the instrument used to inflict harm bears directly on the outcome, and that no weapon of interpersonal violence is more effective, or easier to use, than a gun. As the criminologist Philip Cook wrote, “Guns intensify violence.”

Plainly stated, one would rather face attack with a knife than a gun, not only because the reach of a knife extends only to the length of an attacker’s arm, but because the likelihood of surviving a knife attack is far greater than surviving a gunshot wound. According to one British trauma surgeon, gunshot wounds are “at least twice as lethal as knife injuries and more difficult to repair.”

The second thing Trump doesn’t know, and what the NRA’s ridicule of British “knife control” glosses over, is that in America’s gun-control history, state and local laws typically regulated not only concealed gun carrying, but also knife carrying.

When the colony of New Jersey acted to criminalize the concealed carrying of firearms in 1686, it also included “Daggers, Dirks, Stilladoes.” Louisiana’s 1813 anti-concealed carry law extended to a “dirk, dagger, knife.” Alabama’s 1839 law against the “Evil Practice of Carrying Weapons Secretly” included among the barred weapons “any bowie knife, Arkansas tooth-pick, or any other knife of the like kind.” In 1852, the New Mexico territory barred “carrying short arms such as pistols, daggers, knives, and other deadly weapons, about their persons concealed.”

What these and similar knives had in common was that their blades were usually long and thin, which may have been why they were frequently used in knife fights. By the start of the 20th century, every state but four had criminalized the concealed carry of guns; virtually all of these laws also barred the carrying of fight knives.

In fact, restrictions on knife carrying persist in the United States to the present. In 1958, Congress passed the Federal Switchblade Act, which outlawed the import and interstate trade of knives with spring-loaded blades. The law was revised in 2009 to exclude knives that can be pushed open with one hand. Many states and localities continue to restrict or bar various kinds of knives, although a few states, including Georgia, New Hampshire and Utah, have recently repealed knife restrictions. Repeal efforts even have an organized advocate, Knife Rights Inc.

Despite its current knife attack problem, Britain still maintains a far lower homicide rate than the United States, and we have done nothing to help ourselves with the pell-mell loosening of state concealed-carry restrictions. But we, too, once recognized that guns and knives alike can be used to cause grievous harm to others. It’s neither new nor exceptional.

Robert J. Spitzer

Robert J. Spitzer is chairman of the political science department at SUNY Cortland and author of five books on gun policy, including “Guns Across America: Reconciling Gun Rules and Rights.”