John Quiggen makes an important point. An awful lot of the recent changes in American history can be understood as efforts to graft a proper two-party dynamic onto a country that thanks to both an unusual institutional set-up and the legacy of the Civil War and Jim Crow didn't really have one. The rise of the "New Right" essentially turned the GOP into one half of a two-party system, at which point it became devastatingly effective because the opposition was still behaving like one half of the old, more fluid system. Much recent progressive activism has centered around trying to turn the Democrats into "the other party" of a two-party system.