Mardi Gras night in Mamou, Louisiana, and the main street stage is being broken down. The riders who were triumphantly dancing on horseback this afternon have all gone home to count their bruises. The community gumbo is long gone.

Mamou, for the first time today, is calm.

A few die-hards, however, sit alongside the town’s main intersection. They huddle around a few accordions and fiddles, barely able to hear the hoarse, unamplified cries of the young singer. A black Trans Am with a boom...