All the King's Men, Robert Penn Warren
Warren's Pulitzer Prize-winning 1946 book is almost certainly the most famous novel ever written about politics in America. The main character, Willie Stark, a southern governor who's a populist in public, but a greedy sellout behind the scenes. Warren tells Stark's story through the character Jack Burden, the idealistic narrator and Stark's close assistant, who becomes disillusioned with his boss' willingness to compromise. Stark is based heavily on Huey Long, the former Louisiana governor and senator.