I RECENTLY spent a happy few days in Los Angeles promoting my new book, “Capitalism in America: A History” (co-written with Alan Greenspan). I was driving down Hollywood Boulevard in a taxi thinking that all was right with the world—the sun was shining, the people were good-looking and, above all, I wasn’t on deadline to write something about Brexit—when I caught sight of a giant red billboard bearing a single word in huge letters: BREXIT.