Supersedes Working Paper 23-07 – The Changing Polarization of Party Ideologies: The Role of Sorting

Ideology scores derived from U.S. congressional roll-call voting patterns show that the ideological distance between the two parties along the primary dimension changes inversely with the ideological distance along the secondary dimension. To explain this inverse association, a model of party competition with endogenous party membership and a two-dimensional ideology space is developed. If the distribution of voter preferences is uniform on a disk, equilibrium ideological distances along the two dimensions are inversely related. The model can quantitatively account for the historical movements in ideological distances as a function of changes in the ideological orientation of the two parties.

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