Gerrymandering with Differential Turnout

This paper studies the manipulation of electoral maps by political parties, known as gerrymandering. At the core of our analysis is the recognition that districts must have the same population size but only voters matter for electoral incentives. Using a novel model of gerrymandering that allows for heterogeneity in turnout rates, we show that parties adopt different gerrymandering strategies depending on the turnout rates of their supporters relative to those of their opponents. The broad pattern is to "pack-crack-pack" along the turnout dimension. That is, parties benefit from packing both supporters with a low turnout rate and opponents with a high turnout rate in some districts, while creating districts that mix supporters and opponents with intermediate turnout rates. This framework allows us to derive a number of empirical implications about the link between partisan support, turnout rates, and electoral maps. Using a novel empirical strategy that relies on the comparison of maps proposed by Democrats and Republicans during the 2020 redistricting cycle in the US, we then bring such empirical implications to the data and find support for them.