Political campaigns are increasingly turning to digital advertising to reach voters. It is predicted that, during the 2020 U.S. presidential elections, 28% of political marketing spending will go to online advertising, compared to 20% in 2018 and 0.2% in 2010. Digital advertising platforms’ popularity is partially explained by how they empower advertisers to target messages to platform users with great precision, including through inferences about those users’ political affiliations. However, prior work has shown that platforms’ ad delivery algorithms can selectively deliver ads within these target audiences in ways that can lead to demographic skews along race and gender lines, often without an advertiser’s knowledge.