Pack-Crack-Pack: Gerrymandering with Differential Turnout

This paper studies the manipulation of electoral maps by political parties, commonly referred to as gerrymandering. At the core of our analysis is the recognition that not all inhabitants of a district vote. This is important for gerrymandering as districts must have the same population size, but only voters matter for electoral outcomes. We propose a model of gerrymandering that allows for heterogeneity in voter turnout across individuals. This model reveals a new strategy for the gerrymanderers: the pattern is to pack-crack-pack along the turnout dimension. Specifically, parties benefit from packing low-turnout supporters and high-turnout opponents, while creating cracked districts that combine moderate-to-high-turnout supporters with lower-turnout opponents. These findings yield testable empirical implications about the relationship between partisan support, turnout rates, and electoral maps. Using a novel empirical strategy based on comparing maps proposed by Democrats and Republicans during the 2020 U.S. redistricting cycle, we test these predictions and find supporting evidence.