It all started with Barack Obama. In 2009, white police Sergeant James Crowley arrested a black man for apparently breaking into a house in a prosperous part of Cambridge, Massachussetts. It turned out the black man was Professor Henry Louis Gates Jr: a writer, TV presenter, editor, literary critic, filmmaker and essayist, and the first African American to receive the prestigious Andrew Mellon Foundation Fellowship. He’d lost his keys. Crowley had arrested him for trying to get into his own home.