A Median Activist Theorem for Two-Stage Spatial Models

Abstract

The spatial model of electoral competition has for decades been a staple of formal political theory. As part of this field, a number of authors have developed two-stage spatial models in which electoral candidates must first win intra-party primary elections, and then compete in a general inter-party election. A universal result in these two-stage models is that party selectorates, and in particular the “median party activist”, exert a centrifugal pull on party platforms. The current paper brings this basic finding into question, suggesting that party voters only exert this centrifugal force under fairly strict conditions; and in particular only if candidates attach fairly high value to the outcome. The paper’s primary result, a “Median-Activist Theorem”, suggests that if candidates place little value on winning the nomination in and of itself, primaries are necessary, but not sufficient, for generating more extreme electoral platforms.