If you think US politics is a dirty business now, you ain't seen nothing. Following the US Civil War, politics was violent, personal and sometimes even uncivil. The Day Freedom Died: The Colfax Massacre, the Supreme Court, and the Betrayal of Reconstruction describes one such incident in which a group of white supremacists massacred a group of freedmen and went free.
It's a pretty depressing read at times, considering the attitudes prevalent among the white people of the day. And it's scary to think that those attitudes are still around in some people today.
There were a lot of people discussed in the book, which made it difficult for me to keep everyone straight. At times the story dragged on, but at other times it was riveting.
If you're into this topic, I suspect you would enjoy the book very much.