Incursion and Reclamation in U.S. House Midterm Elections

Not all midterm election gains are created equal. When Republicans swept 63 seats in 2010, they were mostly taking back districts that already leaned in their favor. When Democrats flipped 41 seats in 2018, they were doing something harder – winning in Republican territory. I call these two types of flips reclamation and incursion, and show that the distinction matters for understanding what electoral waves mean and predicting what might happen in 2026. Drawing on Cook PVI data for every midterm House seat that changed party hands from 1998 to 2022, I document a shift from reclamation-dominated waves to incursion-dominated ones – a shift driven by partisan geographic sorting and gerrymandering. I also find that incursion flips revert at higher rates than reclamation flips, which holds implications for understanding the likely durability of party mandates. With the reclamation inventory nearly exhausted, 2026 shapes up as the most incursion-dependent Democratic wave in the post-sorting era.