Dueling incumbent primaries in US House elections

ObjectiveReapportionment and the attendant process of redistricting cause instances where incumbents are faced with the decision to retire or run against a congressional colleague. We investigate two major questions surrounding the previously understudied population of dueling incumbent primaries: First, under what conditions is a dueling incumbent primary likely to manifest? Second, how are dueling incumbent primaries different from the typical primary featuring a single incumbent? MethodsWe address these questions using a novel dataset aggregating descriptive congressional district information on these contests from 1962 to 2016, and separately for 2022. ResultsOur findings show these contests primarily emerge via electoral retrenchment, meaning a state loses representation in reapportionment. Dueling incumbent primaries also arise from the strategic calculations of partisan line drawers. ConclusionsNot only do dueling incumbent primaries comprise a disproportionate share of incumbent defeats, but compared to single incumbent contests, primary duels feature very high redrawn constituencies, voters new to these incumbents, and this reality contributes to the high-risk/reward nature of these rare but electorally consequential contests.