The chronicler of the American twilight is going into semi-retirement. Will Harper’s magazine become less of a lefty echo chamber?Lewis Lapham, the editor of Harper’s, is very old-school. He wears a beautiful dark suit and a necktie tight around his buttoned collar. He not only still smokes (Parliaments, the recherché brand of Bond girls), he smokes in his office. He was educated at Hotchkiss and Yale and Cambridge. His manner, personal as well as literary, is Gore Vidalian, a patrician alloy of faint amusement and grand disappointment. He runs a 155-year-old, self-consciously old-fashioned magazine that’s all about plain text, not...