Jimmy Carter, the country's 39th president, may go down in history as the most prolific head of state and the one with the most bestsellers penned. Simon & Schuster published his latest, Christmas in Plains, with a 400,000 printing. Carter launched his 10-city book tour with appearances on Good Morning America, The View and Charlie Rose. He's also done a 31-city TV satellite tour, a 12-city radio satellite tour and a teleprint conference with eight newspapers. S&S reports that he drew 1,000— 2,000 people at each book signing.