Five Facts on Partisanship and Congressional Districts

The Big InsightWhile gerrymandering is one driver of the polarization in Congress and across the country, self-sorting among voters plays an even larger role.

Most states have now finished drawing the new congressional maps that will be in effect for the next decade, and even though most analysts say neither party is gaining much, criticism of gerrymandering is in full swing. While partisan line-drawing is indeed a problem, however, the main driver of polarization is self-sorting among voters into “Blue” and “Red” enclaves.

1. In 2020, just 37 House races (eight percent of the total) were decided by margins of five points or less, and just 77 (17% of the total) were decided by margins of 10 points or less.

Nationwide, 122 congressional districts lean solidly (by 20 percentage points or more) to one party, while 268 — 62% of the whole House — lean to one party by at least 10 points, according to the Cook Partisan Voting Index. Facts like these are cited in making the case against gerrymandering, but there is more beneath the surface.

2. In nine states, new congressional maps are drawn by independent commissions. Three of the new maps faced court challenges, and one was rejected entirely.

In more than 20 states, some form of commission is used to draw legislative borders, and nine states now have fully independent commissions consisting of non-elected officials. These commissions are intended to reduce partisan motivations in line-drawing. However, while many of these commissions did their jobs effectively this year, the Idaho, Michigan, and Washington maps ended up in court — while in New York, the Legislature rejected the commission’s work and adopted one of the nation’s most gerrymandered maps.

3. Just eight percent of the districts drawn by independent commissions this year are expected to be highly competitive in November — the same share as those drawn by state legislatures.

According to FiveThirtyEight, “commissions’ performance was just so-so” in terms of creating competitive districts. As political scientist Danielle Thomsen has written, when it comes to partisan polarization in Congress, “the academic consensus is that gerrymandering matters anywhere from a little bit to not at all,” with an increasing trend of Democrats wanting to live with Democrats and Republicans wanting to live and associate with Republicans emerging as much more consequential.

4. In 1994, half of Americans said they had an equal number of “liberal” and “conservative” views. In 2017, just one-third did.

It’s not just the district lines that are becoming more partisan — voters themselves are. The Pew Research Center found in 2017 that just 32% said they had a mix of liberal and conservative views, down from 49% in 1994. Moreover, in 1994, 17% of registered Democrats were more conservative than the median Republican; by 2017, the number was just three percent. The numbers were even more stark among Republicans: 23% of them were more liberal than the median Democrat in 1994 — while just one in 100 were by 2017.

5. About 25 million voters live in places where only about one in 10 social encounters is likely to be with someone from the opposite party.

As they become more partisan, voters are also self-sorting politically. Democrats are increasingly moving to urban areas, while Republicans dominate rural America. Even within more politically divided cities and towns, residents tend to cluster into neighborhoods where their neighbors are members of the same political tribe.


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