When trying to put in context how close Donald Trump came to being killed on July 13th, Anthony Cangelosi, a former Secret Service agent, now an academic at the John Jay College of Criminal Justice, uses an analogy that the former president could appreciate. “It’s a chip shot,” he says. For the benefit of non-golfers: one that is easy for somebody who practises. “It’s not hard to hit a target from 150 yards with a rifle,” he says. The shooter, Thomas Matthew Crooks, a 20-year-old from a suburb of Pittsburgh, was a member of a rifle club, though was apparently rejected from his high-school shooting team. Had he been a slightly better shot, America’s election would now look very different. But how on earth was he able to get onto a roof with a view of Mr Trump, and enough time to aim and fire? That question now seems likely to launch an enormous review of presidential security.

The law creating the Secret Service was signed by Abraham Lincoln on April 14th 1865. Unfortunately its original purpose was to take on counterfeiters, not presidential assassins, or else it might have come in handy on that first day—that evening an out-of-work actor shot the president. In fact it turned to protecting presidents only in 1901, after the assassination of William McKinley. Its success has been patchy. Since then, three presidents have been shot: Theodore Roosevelt, John F. Kennedy and Ronald Reagan. Franklin Roosevelt was also almost killed in 1933, and a shooter missed Gerald Ford by inches in 1975. In recent decades, however, the force has grown to 8,000 agents, and no attempt has come so close in 43 years.