The natural question about Apple TV+’s “Manhunt,” based on the book “Manhunt: The 12-Day Chase for Lincoln’s Killer” by James L. Swanson, is going to be “Why now?” It does not seem coincidental that a story that’s essentially about one of the times our democracy was at its most fragile just happens to be coming out during one of the most contentious and divisive election years in U.S.