Democrats and Republicans aren't just polarized. They're segregated.

Race and partisanship have become inseparable forces, and both are driving us apart.

Political polarization is a fact of life in America these days, and it’s not just limited to how far apart the two parties are on the issues. Democrats and Republicans are also very literally far apart from each other in geographic space.

The urban-rural divide that has grown over the past few decades is well-known at this point: Democrats tend to funnel to densely-populated urban areas, Republicans remain in sparse rural areas, with suburbia as a major battleground. I’ve written in this space about some of the many reasons this happens.

Do voters move away from places because of politics?

So Democrats and Republicans live in separate kinds of areas within the country. But the truth, as always, is a little more complicated than that. Even in really one-sided cities and towns, you see low but consistent support for the other party. Donald Trump, for example, won nearly a quarter of the vote in New York City. Joe Biden got beaten badly in the most rural counties and towns in America, but even in those places he enjoyed double-digit support.

Plenty of Republicans live in “Democrat areas”, and vice versa. So are we really all that separate from each other?

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Turns out we are. A few years ago, FiveThirtyEight conducted an extensive analysis of the partisan leanings of America’s major cities. They found that although both Democrats and Republicans do co-inhabit these places, they seem to be doing so under protest, like two siblings forced to sit next to each other in the backseat of the family car.

Here, for example, is FiveThirtyEight’s generated map of my current home, the Boise, Idaho metro area. Democrats tend to cluster in the denser downtown Boise area, especially in the city’s crunchy North End neighborhood.

According to FiveThirtyEight and the political scientists they interviewed, Republicans seek out different parts of American cities:

Across the country, Republicans in urban areas are more likely to be found in the less-centralized, lower-density neighborhoods. “Even if you look within the same census tract or the same ZIP code or the same precinct, and even if you’re in a place like Manhattan, Republicans will search out the less-dense part to live in,” said Steven Webster, a political scientist at Washington University.

This isn’t a great trend for quite a few reasons. Yes, it’s nice to be surrounded by neighbors with similar values, and Americans have every right to do this. But, as I talked about here a couple of weeks ago, it’s still important and comforting for Americans to have some semblance of unifying purpose or common political culture so that we don’t completely fracture apart in a permanent way. This becomes a lot more difficult when, even when we share the same cities, we refuse to share the same space within those cities.

But why is this actually happening? If Democrats and at least some Republicans actually do live in the same cities, how are they still finding their way apart from each other?

There are a ton of complex interlocking reasons, naturally. Some people are moving specifically to live in like-minded places, while others are more naturally sorting into these neighborhoods.

But FiveThirtyEight’s analysis offers some clues as to maybe the most glaring, specific, and rather shameful reason we remain so geographically separate. In their analysis, they used what’s called a Dissimilarity Index, which uses voter data to calculate the extent of voters’ exposure to voters in the other party based on where they live. More simply, the Index tells us how separately a place’s Republican and Democrat residents live from one another, with higher numbers suggesting more partisan segregation. After calculating this figure for America’s largest metropolitan areas, they ranked the most politically polarized major metropolitan areas in the country.

Take a look below at the visualization they compiled, which shows the major cities with the starkest levels of partisan segregation. Notice any similarities?

All but two of the fifteen most politically polarized major urban areas in the country are located in the South. If you expand the analysis beyond just major metropolitan areas, out to all American cities (as political scientist Ryan Enos has) the story is even more stark: every single one of the twenty most party-segregated cities are in the South.

Why is the South so overrepresented in this collection of cities with high geographic polarization? I’ll give you two guesses, but I think you’ll only need one. Let’s see if you’re right by diving deeper on one of the Southern cities on FiveThirtyEight’s list.

The first map below shows the racial makeup of the greater Atlanta, Georgia area, with darker green representing more Black residents; dark blue, white residents; orange, Hispanic/Latino; and red, Asian-American. The second map shows how Atlanta voted in 2016, with bluer areas indicating higher vote share for Hillary Clinton, red for Donald Trump.

First, just eyeballing the two maps on top of each other gives us a window into the extreme correlation between the racial makeup of certain neighborhoods, and the party they choose for president. We may have a vague understanding that Black voters tend to overwhelmingly support Democrats, while white voters are more likely to support Republicans. But these maps are driving home the fact that the partisan segregation exposed by the FiveThirtyEight project and other political scientists is, in many cases, merely an incidental result of racial segregation that persists in American cities. Different racial groups tend to be supportive of different parties; these racial groups continue to live apart from one another; ergo, the parties live apart from one another.

I grew up believing and being taught that racial segregation was a thing of the past. It always felt like such a foreign, bygone era to me—that there was a time when the law did not prohibit businesses, schools, and other spaces from keeping out entire races and ethnicities of Americans. It was unbelievable to me that this was something we allowed during my parents’ lifetimes.

An adulthood spent learning about our country in the academic setting, plus a direct lived experience in a few major American cities, has brought my rosy childhood view of our racial politics into reality. Yes, school and housing segregation is technically against the law, but the maps above by themselves tell us that social segregation between different racial groups has persisted in the South, and is helping drive partisan segregation as well.

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Even in places where the Jim Crow legacy is less pronounced, many of our policymaking decisions have codified and enshrined segregation, often intentionally. Cities like Boston, for example, used policies like red-lining to throttle home values in Black neighborhoods, poisoning them as an investment for both home-buyers and businesses alike for generations. The lasting impacts of these practices have made cities like Boston, Chicago, and Milwaukee—distinctly non-Southern places—some of the most racially segregated cities in America to this day.

Other policy choices do this even when race is not an explicit motivator. The post-World War II construction of the Interstate Highway System, for example, was a genuine marvel of American infrastructure. Modern highways helped to expand metropolitan areas in the postwar era, and shot the nation’s economy into the stratosphere.

This system also made possible the growth and thriving of new American suburbs. Highways enabled a mass residential migration that allowed many Americans to enjoy the benefits of the city, while also having more space in less-populated suburbs without sacrificing commuting time. The overwhelming majority of folks who could afford to make this move were, of course, white; thus, the generational economic and social benefits of highway policy were disproportionately reserved for them.

In addition to transporting some racial subgroups away from the others, roads can be a physical barrier of separation that furthers racial segregation. Take as an example 8 Mile Road, a main artery in the north end of Detroit which readers (at least those around my age) will almost certainly remember from Eminem’s 2002 movie and soundtrack of the same name. According to the Detroit Historical Society,

Eight Mile exists as a physical dividing line, as well as a de-facto psychological and cultural boundary for the region. As the northern border to the City of Detroit, Eight Mile separates the city’s predominately African American urban core from the more white suburbs to the north. Although African-Americans live in communities north of Eight Mile, the sense of separation between the two areas still remains.

The road has served, therefore, as a way of separating—both psychologically and logistically—the Black urban core of Detroit from its whiter residents to the north. Property values, poverty, business investment, crime, and other socioeconomic differences fall along this line. I probably don’t have to spell out which side of the road sees the better end of these trends.

But hard lines in the sand like 8 Mile Road don’t just enforce racial separation. The maps below, similar to the ones above of Atlanta, illustrate the racial, then partisan makeup of Detroit. It’s not labeled, but see if you can spot 8 Mile in the second map.

The greater Detroit, MI area based on 2016 presidential election vote choice. Darker blue areas = heavy support for Hillary Clinton (D). Source: New York Times.

Many elements of the partisan polarization and fragmentation we’ve gone through over the past half-century were, in some ways, inevitable. Humans have natural tendencies to sort residentially alongside people who are like them, and race is an important part of people’s identity. So, too, are Americans’ partisan identities. As a result, we see in these maps a similar kind of reflection that we saw with Atlanta above.

But the harrowing separation produced by 8 Mile tells us that this segregation wasn’t all an accident, and it wasn’t all inevitable. We’ve made policy and infrastructure decisions over the course of our history with both intended and unintended racial impacts that could have been avoided, but weren’t. We’re separated not just naturally by our identities, beliefs, and skin colors, but purposely by the literal barriers we choose to put between us.

This does not mean, of course, that race is the sole driver of partisan segregation. As I wrote about a couple of weeks ago, political nationalization and partisan sorting is a process that encompasses all sorts of other identities like socioeconomic status, religion, and educational attainment. For example, we saw above that the Boise, Idaho metropolitan area is also quite segregated on a partisan basis, even though the metro area as a whole is about 90% White.

What we see in Boise is essentially a whole lot of White voters that still are segregated based on party for reasons not having to do much with race. But the stark nature of the geographic divisions we see in Detroit in other areas—and the fact that our policymaking decisions have helped keep these barriers in place—should inspire us to think a little harder and more honestly about the twin roles race and partisanship play in our politics.