Explaining Subnational Constitutional Choices: Separation of Powers in the American States

Why do US states—operating under a shared federal framework—nonetheless diverge, or converge, in separation-of-powers design? Scholarship on subnational constitutionalism rarely offers inference-oriented, large-N tests of competing explanations for subnational institutional patterns. We address this gap by coding forty-five core separation-of-powers features across all fifty states and analyzing both feature-level choices and overall interstate similarities. We evaluate hypotheses based on political culture, constitutional history, ideology and partisanship, sociodemographic variables, and textual similarity. We find that constitution age, borrowing, and text explain similarity in constitutional provisions, ideological profile predicts convergence in legislation and jurisprudence, and feature dates, ideology, and urbanization best explain individual features. Urban, liberal, Democrat-leaning states adopt arrangements that facilitate high-capacity activist government (strong governors and legislatures, functionalist constitutional interpretation), while Southern, conservative, Republican-leaning states favor stricter, formalist separation of powers while weakening both political branches.