The pattern was always the same. There was one group of readers who bought conservative books and another that supported liberal authors. The maps Krebs made of Americans' book-buying patterns pictured two swarms: liberals on one side and conservatives on the other.
There were always one or two books in the middle-books both sides read, connector books between readers who otherwise had little in common. In Krebs' first map in 2003, the connector book was What Went Wrong, Bernard Lewis' book on the Islamic world. The books in the middle would change with the times, but there was always something both sides were reading in common.
Until last week.
The Big Sort : America's Partisan Reading List