If this isn't a matter of national security, what is? When 13 people end up dead at a US military base, that surely crosses the threshold – putting America's problem with guns into the category reserved for threats to the mortal safety of the nation. At its narrowest, Monday's massacre at the Washington navy yard is a national security issue because it involved hostile entry into what was meant to be a secure military facility. Plenty will now focus on how a man twice arrested in gun-related incidents was able to gain such easy access to the nerve centre of the US navy. There will be inquiries into the entry-pass system, use of contractors and the like.

But that would be to miss the wider point. America's gun sickness – which has turned massacres of this kind into a fairly regular, rather than exceptionally rare occurrence – endangers the US not solely because it can lead military personnel to lose their lives, nor even because it can lead to the murder of schoolchildren, as it did at Sandy Hook elementary school last year, or the death of young movie-goers, as it did in Aurora, Colorado, also last year – dreadful though those losses are.

The foreign policy experts who gather in the thinktanks and congressional offices not far from the navy yard often define national security to encompass anything that touches on America's standing in the world. That ranges from its ability to project military force across the globe to its attractiveness, its "soft power". For decades, this latter quality has been seen as one of the US's primary assets, central to its ability to lead and persuade other nations.

But America's gun disease diminishes its soft power. It makes the country seem less like a model and more like a basket case, afflicted by a pathology other nations strive to avoid. When similar gun massacres have struck elsewhere – including in Britain – lawmakers have acted swiftly to tighten controls, watching as the gun crime statistics then fell. In the decade after the rules were toughened in Australia in 1996, for example, firearm-related homicides fell by 59%, while suicides involving guns fell by 65%.

But the US stays stubbornly where it is, refusing to act. When President Obama last tried, following the deaths of 20 children and six staff at Sandy Hook at the end of 2012, his bill fell at the first senate hurdle. He had not proposed banning a single weapon or bullet – merely expanding the background checks required of someone wanting to buy a gun. But even that was too much. The national security pundits who worry how a US president is perceived when he is incapable of protecting the lives of innocent Syrians abroad should think how it looks when he is incapable of protecting the lives of innocent Americans at home.

On guns, the US – so often the world leader in innovation and endeavour – is the laggard, stuck at the bottom of the global class. Bill Clinton perfectly distilled the essence of soft power when he said in 2008, "People the world over have always been more impressed by the power of our example than by the example of our power." He was right. But every time a disturbed or angry individual is able to vent his rage with an assault weapon, killing innocents with ease, the power of America's example fades a little more.

@Freedland