Gerrymandering and geographic polarization have reduced electoral competition
Abstract
Changes in political geography and electoral district boundaries shape representation in the United States Congress. To disentangle the effects of geography and gerrymandering, we generate a large ensemble of alternative redistricting plans that follow each state's legal criteria. Comparing enacted plans to these simulations reveals partisan bias, while changes in the simulated plans over time identify shifts in political geography. Our analysis shows that geographic polarization has intensified between 2010 and 2020: Republicans improved their standing in rural and rural-suburban areas, while Democrats further gained in urban districts. These shifts offset nationally, reducing the Republican geographic advantage from 14 to 10 seats. Additionally, pro-Democratic gerrymandering in 2020 counteracted earlier Republican efforts, reducing the GOP redistricting advantage by two seats. In total, the pro-Republican bias declined from 16 to 10 seats. Crucially, shifts in political geography and gerrymandering reduced the number of highly competitive districts by over 25%, with geographic polarization driving most of the decline.
Keywords
Cite
@article{arxiv.2508.15885,
title = {Gerrymandering and geographic polarization have reduced electoral competition},
author = {Ethan Jasny and Christopher T. Kenny and Cory McCartan and Tyler Simko and Melissa Wu and Michael Y. Zhao and Aneetej Arora and Emma Ebowe and Philip O'Sullivan and Taran Samarth and Kosuke Imai},
journal= {arXiv preprint arXiv:2508.15885},
year = {2025}
}
Comments
8 pages, 2 figures, plus appendices and references