Expressive motives and third-party candidates

The electoral success of an extremist party usually attracts considerable attention. Yet, they rarely have an opportunity to directly influence policy as they are, more often than not, shut out of the policy-making process by mainstream parties. Extremist parties may, however, influence policy indirectly by inducing mainstream parties to adjust their electoral strategies. I consider a model of electoral competition between an expressive extremist party and two mainstream parties in first-past-the-post and majority runoff elections. The presence of an extremist party results in an equilibrium policy outcome that is further away from the extremist's preferred policy but the magnitude of the effect is shown to depend on the type of electoral system.