Fifteen years after Ronald Reagan’s diagnosis of Alzheimer’s, and five years after his death, Nancy Reagan has triumphed over loneliness, grief, and a bad fall last year. At the former First Lady’s house, in Bel Air, California, the author gets her to sit down for a rare in-depth interview, covering the part she played in her husband’s White House, her dealings with the Bushes and Obamas, and her fight for stem-cell research.