Durable Majority Gerrymanders: Where Partisan Gerrymandering can Displace Democracy

We develop the concept of, and estimation tools for, durable majority gerrymanders: electoral district maps drawn to reduce an opposing political party’s probability of winning a majority in a legislative chamber. Directly interpretable, forward-looking, and motivated by the democratic principle that a party in power should have some chance of losing it, this measure provides new insights into the role of redistricting in state legislative elections. We show that, when map drawers are unconstrained, the ability to create durable majorities is so widespread that at least one party in every state can draw a map where a majority of legislative districts withstand almost any likely future electoral swing. Enacted maps are less durable, due to a combination of underlying geography, voter partisanship, and state-level guidelines. This paper provides the theoretical framework and empirical tools to understand which gerrymandered maps enable state-level majorities to emerge and to endure.