The top headline of The New York Times front page of July 18 was thoroughly predictable: "Attack on Officers Jolts a Nation on Edge." The previous day three policemen had been shot dead in Baton Rouge, Louisiana. Less than 10 days earlier, on July 8, five officers had met the same fate in Dallas.

These killings of policemen — both by former servicemen — were direct reactions to the recent, sensational spate of police officers killing citizens. I say "sensational" because these murders happened to be digitally recorded and broadcast via social media. One of them occurred in the same city, Baton Rouge, on July 5, with a video showing two policemen wrestling a man to the concrete of a parking lot, then shooting him dead.

Most killings of citizens by law enforcement officers do not attract such national attention, but the number should shock any other "civilized" society. It totaled 990 in 2015, according to "Fatal Force," a database that The Washington Post set up last year to catalog "every fatal shooting nationwide by a police officer in the line of duty." It is updated daily. For a listing of individual victims, there is another site, "Killed By Police." It was established in May 2013. It is also updated every day.