Stemming the Tide: The Impact of Redistricting on the 2018 Midterm Election

In the 2018 election, the Democratic Party rode a midterm wave to win a majority in the US House of Representatives. Throughout the campaign and its aftermath, a great deal of attention has been paid to the effects of gerrymandering, sorting, and district boundaries on the outcome of House races. We assess the impact of current district boundaries on electoral outcomes, using actual election results from 2018 alongside those generated by a simulation technique that relies upon advanced geographic information systems (GIS) and principles of graph theory. We find that redistricting practices in Republican-drawn states were at least partially effective in stemming the blue wave, allowing them to hold more seats than we would otherwise expect. Finally, we demonstrate that the insulating properties of Republican redistricting efforts also impacted the makeup of state legislatures, which could impact House redistricting in 2020.