Mitt Romney was on the David Letterman show last week and hit a home run. It was two white guys from the Midwest, born in 1947, chatting amiably about the icons of yesteryear: Earl Scheib, the car-painting magnate; the Studebaker (a car, for you younger readers) and the Rambler Classic, manufactured by AMC, the automobile company managed by Mitt’s father, George. AMC and Studebaker were wiped from the face of the earth by better cars made in Japan by more diligent workers, although that is not a subject that came up. Letterman saved the last minute of Romney’s appearance for...