Lucy, by Ellen FeldmanRead about the other entries on the list.
[T]his novel is about a president who was in love with someone who wasn’t his wife. Before he was President, Franklin Delano Roosevelt loved Lucy Mercer…Eleanor’s social secretary. Through polio, a world war, and two presidential terms, despite his promises to Eleanor, Franklin and Lucy remain connected. Heartbreaking, romantic, and beautiful.
Also see: Jeff Somers's list of six insane fictional presidents and David Daw's five American presidents in alternate history.
--Marshal Zeringue