After Alexander : Race, Partisanship, and Partisan Gerrymandering

In May 2024, the U.S. Supreme Court issued a key racial gerrymandering decision in Alexander v. South Carolina NAACP . At issue was whether South Carolina’s mapmakers selected precincts for the redrawn first congressional district based on their racial composition or partisanship. In overturning the district court’s conclusion that the state's 1st congressional district (CD #1) was a racial gerrymander, Justice Alito argued that mapmakers have no reason to use racial data when drawing districts to favor one party: they simply need partisan data. Justice Kagan challenged this claim, arguing in her dissent that racial data can yield a superior partisan gerrymander. We evaluate these competing claims with an original longitudinal dataset of precinct election results in South Carolina from 2010 to 2020. Our analysis allows us to assess how well a precinct’s racial and partisan makeup in the election before redistricting explains election results over the subsequent decade. We find that the use of race, although potentially unlawful, can significantly help mapmakers predict future election outcomes. Not only does race improve post-redistricting election forecasts—even when controlling for partisanship—but also the analysis reveals (1) precinct race has a substantively large effect on future election results and (2) race is a more stable predictor compared to party. Our findings suggest that state legislatures, particularly those with demographics like South Carolina, have good reason to rely on racial data when drawing partisan districts, either alone as a proxy for partisanship or in combination with partisan data. We believe this article provides much-needed insight into a key issue for future racial gerrymandering and voting rights litigation.