The regularity of mass killings breeds familiarity. The rhythms of grief and outrage that accompany them become — for those not directly affected by tragedy — ritualised and then blend into the background noise. That normalisation makes it ever less likely that America’s political system will groan into action to take steps to reduce their frequency or deadliness. Those who live in America, or visit it, might do best to regard them the way one regards air pollution in China: an endemic local health hazard which, for deep-rooted cultural, social, economic and political reasons, the country is incapable of addressing. This may, however, be a bit unfair. China seems to be making progress on pollution.