Traditionally, four horsemen presage the apocalypse. A little before 11am on September 6th Donald Trump posted a picture of himself imposed on a poster for the movie “Apocalypse Now” with the line: “Chicago about to find out why it’s called the Department of WAR.” An hour later, in Pilsen, a Latino neighbourhood on the south-west side of the city, the annual Mexican Independence Day parade began with four men on horseback.