Tim Miller is a former Republican communications operative who held moderate views and backed moderate candidates for years. But he says in practicing the dark arts of opposition research and planting negative stories about rival candidates, he worked with increasingly extreme right-wing media outlets and fed populist outrage that would radicalize much of the Republican voter base. Miller examines his past work, and considers why so many Republicans who thought Trump unfit for office nonetheless backed him, in a new book, called Why We Did It.