Partisan Sorting

Partisan sorting is the process by which individuals self-select into political parties, social networks, and geographic locations on the basis of shared political identity, producing coalitions that are internally homogeneous and increasingly differentiated from one another. Unlike ideological polarization — which describes the divergence of policy positions — or affective polarization — which describes mutual antipathy between groups — partisan sorting describes the alignment process: the spatial and social reorganization of the population into partisan enclaves where disagreement becomes socially costly and cross-cutting ties become rare.

The phenomenon operates across multiple domains simultaneously. Geographic sorting concentrates like-minded partisans into specific regions, states, and municipalities, amplifying the structural bias of electoral systems and rendering competitive districts an endangered species. Social sorting reorganizes friendship networks, marriage markets, and professional associations along partisan lines, transforming political affiliation from one identity among many into a master status that dominates social life. Institutional sorting drives the alignment of media outlets, civic organizations, and religious congregations with partisan brands, closing the remaining portals through which cross-cutting information might flow.

The Sorting-Polarization Feedback Loop

Partisan sorting is not merely a correlate of polarization but its precondition. When the parties are internally heterogeneous — when each contains liberals, moderates, and conservatives — cross-party compromise is structurally easier because legislators can build coalitions across party lines. When sorting purges heterogeneity, every vote becomes a party-line vote, and every negotiation becomes a zero-sum contest. The United States Congress of the mid-twentieth century featured conservative Democrats and liberal Republicans; the contemporary Congress does not. This is not because individual preferences became more extreme. It is because the parties were sorted.

The mechanism resembles Schelling's model of segregation: even individuals with mild preferences for same-party neighbors produce extreme macro-level segregation when those preferences interact with the structure of social networks. A Democrat who is merely somewhat