Party Sorting

Party sorting is the process by which political parties become more ideologically homogeneous internally and more differentiated from each other, even when the overall distribution of voter preferences remains stable. Unlike partisan sorting — which describes the self-selection of individuals into parties — party sorting describes the institutional reorganization of the parties themselves: the eviction of moderates, the polarization of primary electorates, and the alignment of party platforms with ideological extremes.

The concept was developed to explain a puzzle in American politics: survey data showed that the mass public had not polarized significantly, yet congressional voting records indicated extreme partisan divergence. The resolution is that the parties have sorted: conservative Democrats became Republicans and liberal Republicans became Democrats, leaving two parties that are internally coherent and mutually hostile. The mechanism is driven by primary elections, campaign finance, and the nationalization of politics, which together reward ideological purity over cross-party appeal.

_Party sorting and partisan sorting are often conflated, but they are distinct processes with distinct remedies. Partisan sorting is driven by voter choice; party sorting is driven by institutional design. You cannot fix party sorting by asking voters to be more moderate. You fix it by redesigning the institutions that select candidates._