Identical geography, different party: a natural experiment on the magnitude of party differences in the U.S. Senate 1960-1984

Inspired by Downs (1957), dozens of articles have been written in which party competition is modelled as a battle by office-seeking politicians for the allegiance of the median voter (see reviews in Riker and Ordeshook, 1973; Enelow and Hinich, 1984). Yet the critical implications which derive from this median voter mode, namely Tweedledum and Tweedledee politics and politically competitive elections, are falsified by the data.