At FiveThirtyEight, Harry Enten asks why there are fewer competitive districts.
Gerrymandering is part of the story. Take a look at the interactive graphic we built to demonstrate how congressional district lines shift when they are drawn to prioritize different goals. It’s clear that most redistricting schemes that ignore politics and race would yield more competitive U.S. House districts — i.e., those with a partisan lean of 10 percentage points or less — than we currently have. But our analysis suggests that the relative lack of competitive seats under the current map can’t be explained by gerrymandering alone. Under the two redistricting schemes in our interactive that attempt to draw districts to be compact in shape, there are roughly 30 more competitive districts than there are under the current congressional map. That doesn’t come close to taking into account the loss of 92 similarly competitive districts between 1996 and 2016.4FiveThirtyEight contributor David Wasserman and Ally Flinn calculated that only 17 percent of the decline in competitive districts over the past 20 years was the result of redistricting.
So if the redistricting process isn’t solely to blame, what else is going on? It’s actually pretty simple: The states, counties and even neighborhoods from which districts are drawn are less competitive than they used to be because voters are sorting themselves. People are changing their political opinions to be more like their neighbors’, and people are moving to regions where their political viewpoint is more common. This “self-sorting” means more and more areas come, in essence, pre-gerrymandered — dominated by partisans. That makes it more difficult to draw competitive districts without an increased effort to do so.