There were lots of mixed messages that came out of this election. Pres. Donald Trump's divisive and polarizing style cost him the White House, but his unpopularity didn't doom down-ballot Republicans. Trump's attacks on Joe Biden as a secret supporter of socialism fell flat, but that didn't insulate House Democratic candidates from being portrayed as such. And then, there are the suburbs. They were the linchpin of Biden's victory, but failed to deliver success for House Democrats in states like Texas, Missouri, Ohio or Indiana. 

We don't have all the data yet, but it seems as if, once again, density was the dividing line between blue and red suburbs. 

In the wake of the 2012 election, Democrats found success in the suburbs nestled next to major metro areas. But, less densely populated suburban areas remained red. David Troy, a software engineer, plotted the results and found that "At about 800 people per square mile, people switch from voting primarily Republican to voting primarily Democratic. Put another way, below 800 people per square mile, there is a 66% chance that you voted Republican. Above 800 people per square mile, there is a 66% chance that you voted Democrat." 

In his 2019 paper, "The Suburbanization of the Democratic Party, 1992–2018," Boston College political science professor David Hopkins found a similar density divide. "Democratic suburban growth has been especially concentrated in the nation's largest metropolitan areas, reflecting the combined presence of both relatively liberal whites (across education levels) and substantial minority populations, but suburbs elsewhere remain decidedly, even increasingly, Republican in their collective partisan alignment. Rather than stimulating a broad national pro-Democratic backlash across suburban communities in general, as is sometimes suggested by political observers, the election of Donald Trump has instead further magnified this existing divergence—leaving American suburbia, like the nation itself, closely and deeply divided between the two major parties." 

So, what did the density divide look like this year?

An excellent first draft analysis of the (still incomplete) county data by Bloomberg/City Lab found the tipping point to be 700 people per square mile. "Most of the red counties have densities of fewer than 500 people per square mile. Most of the purple counties are clustered at densities of between 400 and 1,500 people per square mile. And the blue counties are those above 1,500 people per square mile. While there are notable exceptions to this pattern, the basic trend suggests the dominant role suburban density plays in American political life." 

To me, the most interesting takeaway from this analysis was the designation of 'purple counties' — those counties that are more exurban than suburban. In fast-growing swing states like Texas, North Carolina and Georgia, how these areas vote will determine which party wins those states in the future.

To check how those 'purple counties' performed this year, I checked in on six of them. In North Carolina, I looked at Alamance County, which is wedged in the fast-growing Research Triangle between Greensboro and Durham, and Cabarrus County, located northeast of Charlotte. In Georgia, I looked at two exurban counties north of Atlanta — Forsyth and Cherokee. In Texas, it was Denton and Collin Counties — the northern exurbs of the ever-sprawling Dallas-Ft. Worth Metroplex. 

All of these counties were deep red in 2012 and 2016. However, this year, while Trump carried every one of them, it was by a lower margin than he saw just four years earlier. 

For example, in 2016, Trump carried Cabarrus County (population density 599 people per square mile) by 20-points (58-38 percent). This year, he won it by just 9 points (54-45 percent). In smaller Alamance County (400 ppl/square mile), Trump's margin narrowed by 5 points (from +13 to +8).

Everything is bigger in Texas, even the vote swings. In 2012, Mitt Romney carried Denton (Flower Mound) and Collin (Plano) by just over 30 points. This year, Trump took Collin by just 4 points (51-47 percent) and Denton by 8 points (53-45 percent). Both counties are hovering close to the 1,500 people/square mile density that Bloomberg/City Lab identified when a county turns blue. 

In Georgia, the exurbs are getting less red, but they aren't purple. Trump carried Cherokee County by 40 points (69 percent to 29 percent). Even so, it's a 10-point drop from Trump's 73-23 percent showing four years earlier. In Forsyth — the fastest growing county in the state — the GOP margin has shrunk 29 points since 2012 (from +63 to +34). 

GOP Margin Shifts in 'Purple Counties'

This Democratic headway into fast-growing exurbs represents a serious threat to the GOP grip on these sunbelt states. As Dante Chinni, a political analyst for the Wall Street Journal and NBC and expert on the geographic distribution of the vote, argued in his recent analysis of the 2020 election: "Republican candidates need big margins out of those exurb counties to help offset the Democrats big wins in the urban suburbs and big cities." And, as we've seen in states like Virginia, once these exurbs start to turn blue, they don't turn back. Northern Virginia's Loudoun County flipped red to blue in 2008, with Obama carrying this county by 8 points. In 2020, Biden carried the once rural county by 25 points. 

But, we also know that Virginia has behaved much differently than its neighbors to the south. There are many reasons for this, but one big difference between Virginia and other sunbelt/southern states is that the state as a whole and its northern suburbs have a more highly educated population. For example, 38 percent of Virginia residents have a college degree, compared to just 31 percent in Georgia and North Carolina, and 29 percent in Texas. Loudoun County, Virginia has twice as many college graduates as Cabarrus County in exurban Charlotte (60 percent to 31 percent). 

We do know that these suburbs were moving in the Democrats' direction pre-Trump. What we don't know is if the pace of that realignment will continue to be as significant when Trump is no longer in the White House. 

More from the Cook Political Report

First Person
Cook Politcal Logo