Replication Data for: The Rule, Not the Exception: One-Party Monopolies in the American States

Thousands of studies have examined party competition in the American states, finding significant consequences for voter turnout, policy adoptions, and more. Long-term patterns of party control have received comparatively less attention. Here, we reexamine the time-honored conversation about the operationalization of party competition. We then update Klarner’s Ranney-inspired state partisan balance data to include state house composition, state senate composition, and gubernatorial vote share since the 1930s, adding – in light of the nationalization of American politics – presidential vote share and the proportion of Democrats in each state’s congressional delegation. After establishing a threshold for one-party dominance, we examine the frequency and duration of subnational party monopolies, highlighting regional variations in the relationship between the state and national measures and applying the index to voter turnout. Our analysis reveals that extended periods of one-party dominance are the rule rather than the exception in the American states, are currently experiencing a dramatic resurgence, and are thus a phenomenon ripe for further exploration.