IF YOU have to pick a single city to illustrate the precipitous economic decline of America’s rust belt, look no further than Flint, Michigan. “Vehicle City”, as it is nicknamed, used to be home to one the biggest car-factory hubs in the country. But as American manufacturing jobs disappeared, Flint’s economy collapsed. In April 2014 the city’s financial woes spawned a public-health crisis. Desperate to cut costs, Flint’s cash-strapped municipal government switched its water supplier from the Detroit Water and Sewage Department, which takes its water from Lake Huron, to the Flint River. Unfortunately, the new water supply was contaminated with high levels of lead, a highly toxic element that can cause health problems ranging from heart disease to brain damage.