In 1999, there were 164 House districts where election results were within five points of the national popular vote. Today there are only 82. One major factor in the elimination of competitive swing districts is gerrymandering, which could have a decisive impact on which party controls the House of Representatives in 2025.

The Cook Political Report defines swing districts as those in which the election results are within five points of the nation's overall vote. For example, if the national vote is 50% for Republicans and 50% for Democrats, a swing seat would be any seat where the district voted within five points of the national vote in favor of either party. Over the past 25 years, however, the number of competitive districts has been cut in half. Beyond just the shrinking number of total competitive seats, many of the competitive seats are located in just two states: New York and California.

According to Jonathan Cervas, a professor at Carnegie Mellon University and redistricting consultant, redistricting — when states redraw their congressional districts every ten years — is a key part of the decline in competitive House races and has been for decades. Because voters are “not very persuadable,” redistricting has become a “primary method” by which parties can gain or lose seats in Congress, he explained. Since the 2010s partisan redistricting, or gerrymandering, has resulted in relatively few competitive House races.

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