ONE day after 14 people died and 21 were injured in a mass shooting in San Bernardino, California, America's Senate defeated a bill that would have prevented people on the terror watch list from buying guns. Making things a bit more difficult for people bent on killing Americans might sound like a rather moderate reform. But 54 conservative senators determined that such a rule might impinge on the gun rights of innocent Americans who were mistakenly placed on the watch-list—a risk assessment that is hard to square with the calculus used by many of the same lawmakers who oppose resettling Syrian refugees lest one of them turn into a terrorist. In the wake of the school shooting in Newtown, Connecticut that killed 20 children and 6 staff members in 2012, a bipartisan bill to enhance background checks for gun purchasers came up a few votes short. It was voted down last week as well. It seems even the mildest measure to curb guns in America is doomed to fail. Why has Congress found it impossible to pass gun-control legislation in the wake of a grim drumbeat of mass killings? Many people attribute the phenomenon to the power of the National Rifle Association (NRA), one of America’s richest and most influential lobbying groups. But there is more to the story. The NRA builds its prestige on a constituency that is more strident and more politically active than proponents of gun-control. So while 55% of Americans believe that gun laws should be “more strict” (as compared to 11% who want them to be “less strict” and 33% who are satisfied with the laws as they stand), gun owners are twice as likely to sound off to their congressmen and nearly five times more apt to contribute money to candidates or interest groups that reflect their views on guns. America’s electoral structure also lends NRA supporters outsize influence. As many gun-rights advocates live in rural areas where a few votes can swing a congressional election, “[t]he NRA's job is made easier,” Stephen Hill and Robert Richie write. The group “can target its resources at the three dozen swing districts like a military strategist dividing quadrants on a battlefield”.

Opponents of gun control routinely argue that the Second Amendment’s “right to bear arms” ensures unfettered access to guns. Seven years ago, the Supreme Court ruled that a ban on handguns in the home was an affront to the Second Amendment. But since the ruling in District of Columbia v Heller, the justices have refused to embellish this right. On December 7th, the Court declined to hear a case challenging the constitutionality of a law in Illinois that banned semi-automatic assault rifles and large-capacity magazines. Only two justices dissented from this refusal, indicating that a solid majority on the Supreme Court would vote to uphold many gun regulations that Congress may yet pass.

Recent mass shootings may mobilise advocates of gun restrictions and could conceivably even spur legislators to reinstate the assault weapons ban that expired in 2004 or pursue other gun legislation. But there is reason to wonder how much of a difference these reforms would make. American civilians own far more guns than anybody else in the world. The land of the free is home to an estimated 270m guns, enough for nearly nine in ten Americans. (That’s compared to 46m guns for the runner-up, India, with a population quadruple that of America.) So even if all new gun purchases were banned tomorrow, there are enough rifles floating around the country to fuel countless more mass shootings. Some countries, notably Australia, have rounded up privately owned weapons and seen a dramatic decline in suicides and homicides. But no one in America is proposing such a radical solution to its rash of tragic shootings.