Power sharing and electoral equilibrium

This paper considers a model of (consensual) democracy where political parties engage first in electoral competition, and they share policy-making power afterward according with the votes gathered in the election. The paper uncovers the difficulties to guarantee stability in this institutional setting; and it provides a condition of symmetry on parties’ political motivations that ensures the existence of pure strategy equilibrium under a broad family of power sharing rules, ranging from fully proportional to winner-take-all. The equilibrium analysis shows that power sharing and ideology exert a centrifugal force on policy platforms that increases party polarization, with the paradoxical result that consensual democracies can actually lead to more radical electoral campaigns than winner-take-all.