HOUSTON — FUTURE historians of France may well decide that the Fifth Republic died as it was born: in a traffic incident.

As France and much of the world now know, part of President François Hollande’s morning routine of late has been to zip on his moped between the Élysée Palace and an apartment on the aptly named Rue du Cirque for romantic trysts with the actress Julie Gayet. While his partner, Valérie Trierweiler, and his interior minister, Manuel Valls, were unaware of these jaunts, the paparazzi, cameras trained on the building, shot a helmeted Mr. Hollande entering and leaving by the front door.

So much of this affair is so foreign to Americans. We are not accustomed to presidents astride mopeds, just as our presidents are not accustomed to the public’s indifference to their private affairs. (Yes, despite all the attention, more than three-quarters of the French still believe this affair is none of their affair.)

The Affaire Hollande, however, is increasingly foreign to the French, as well — at least for those who recall an earlier traffic incident. In late August 1962, near a suburban traffic circle called Petit-Clamart, President Charles de Gaulle was riding with his wife and son-in-law when assassins, machine guns trained on the presidential Citroën, raked it with bullets. Miraculously, everyone, including the chickens Mme. de Gaulle had put in the trunk, survived unscathed....