Keith T. Poole and Howard Rosenthal have analyzed 16 million individual roll call votes spanning the two centuries since the two Houses of Congress began recording votes in 1789. By tracing the voting patterns of Congress throughout the country's history, Poole and Rosenthal find that, despite a wide array of issues facing legislators, over 80% of a legislator's voting decisions can be attributed to a consistent ideological position ranging from ultraconservatism...