Control of the House of Representatives could teeter precariously for years as each party consolidates its dominance over mirror-image demographic strongholds.

That’s the clearest conclusion of a new analysis of the demographic and economic characteristics of all 435 congressional districts, conducted by the Equity Research Institute at the University of Southern California in conjunction with The Atlantic.

Based on census data, the analysis finds that Democrats now hold a commanding edge over the GOP in seats where the share of residents who are nonwhite, the share of white adults with a college degree, or both, are higher than the level in the nation overall. But Republicans hold a lopsided lead in the districts where the share of racial minorities and whites with at least a four-year college degree are both lower than the national level—and that is the largest single bloc of districts in the House.

This demographic divide has produced a near-partisan stalemate, with Republicans in the new Congress holding the same narrow 222-seat majority that Democrats had in the last one. Both sides will struggle to build a much bigger majority without demonstrating more capacity to win seats whose demographic and economic profile has mostly favored the other. “The coalitions are quite stretched to their limits, so there is just not a lot of space for expansion,” says Lee Drutman, a senior fellow in the political-reform program at New America.

The widening chasm between the characteristics of the districts held by each party has left the House not only closely divided, but also deeply divided.

Through the late 20th and early 21st centuries, substantial overlap remained between the kinds of districts each party held. In those years, large numbers of Democrats still represented mostly white, low-income rural and small-town districts with few college graduates, and a cohort of Republicans held well-educated, affluent suburban districts. That overlap didn’t prevent the House from growing more partisan and confrontational, but it did temper that trend, because the small-town “blue dog” Democrats and suburban “gypsy moth” Republicans were often the members open to working across party lines.

Now the parties represent districts more consistently divided along lines of demography, economic status, and geography, which makes finding common ground difficult. The parties’ intensifying separation “is a recipe for polarization,” Manuel Pastor, a sociology professor at USC and the director of the Equity Research Institute, told me.

To understand the social and economic characteristics of the House seats held by each party, Jeffer Giang and Justin Scoggins of the Equity Research Institute analyzed five-year summary results through 2020 from the Census Bureau’s American Community Survey.

The analysis revealed that along every key economic and demographic dimension, the two parties are now sorted to the extreme in the House districts they represent. “These people are coming to Washington not from different districts, but frankly different planets,” says former Representative Steve Israel, who chaired the Democratic Congressional Campaign Committee.

Among the key distinctions:

*More than three-fifths of House Democrats hold districts where the share of the nonwhite population exceeds the national level of 40 percent. Four-fifths of House Republicans hold districts in which the minority share of the population is below the national level.

*Nearly three-fourths of House Democrats represent districts where the share of white adults with a college degree exceeds the national level of 36 percent. More than three-fourths of Republicans hold districts where the share of white college graduates trails the national level.

*Just over three-fifths of House Democrats hold districts where the share of immigrants exceeds the national level of 14 percent; well over four-fifths of House Republicans hold districts with fewer immigrants than average.

*Perhaps most strikingly, three-fifths of Democrats now hold districts where the median income exceeds the national level of nearly $65,000; more than two-thirds of Republicans hold districts where the median income falls beneath the national level.

Sorting congressional districts by racial diversity and education produces the “four quadrants of Congress”: districts with high levels of racial diversity and white education (“hi-hi” districts), districts with high levels of racial diversity and low levels of white education (“hi-lo districts”), districts with low levels of diversity and high levels of white education (“lo-hi districts”), and districts with low levels of diversity and white education (“lo-lo districts”). (The analysis focuses on the education level among whites, and not the entire population, because education is a more significant difference in the political behavior of white voters than of minority groups.)

Looking at the House through that lens shows that the GOP has become enormously dependent on one type of seat: the “lo-lo” districts revolving around white voters without a college degree. Republicans hold 142 districts in that category (making up nearly two-thirds of the party’s House seats), compared with just 21 for Democrats.

The intense Republican reliance on this single type of mostly white, blue-collar district helps explain why the energy in the party over recent years has shifted from the small-government arguments that drove the GOP in the Reagan era toward the unremitting culture-war focus pursued by Donald Trump and Florida Governor Ron DeSantis. Many of the most militantly conservative House Republicans represent these “lo-lo” districts—a list that includes Marjorie Taylor Greene of Georgia, Lauren Boebert of Colorado, Matt Gaetz of Florida, Ralph Norman of South Carolina, and Scott Perry of Pennsylvania.

“The right accuses the left of identity politics, when the analysis of this data suggests that identity politics has become the core of the Republican Party,” Pastor told me.

House Democrats are not nearly as reliant on seats from any one of the four quadrants. Apart from the lo-lo districts, they lead the GOP in the other three groupings. Democrats hold a narrow 37–30 lead over Republicans in the seats with high levels of diversity and few white college graduates (the “hi-lo” districts). These seats include many prominent Democrats representing predominantly minority areas, including Jim Clyburn of South Carolina, Terri Sewell of Alabama, and Ruben Gallego of Arizona. At the same time, these districts have been a source of growth for Republicans: The current Democratic lead of seven seats is way down from the party’s 28-seat advantage in 2009.

Democrats hold a more comfortable 57–35 edge in the “lo-hi” districts with fewer minorities and a higher share of white adults with college degrees than average. These are the mostly white-collar districts represented by leading suburban Democrats, many of them moderates, such as Angie Craig of Minnesota, Seth Moulton of Massachusetts, Sharice Davids of Kansas, and Mikie Sherrill of New Jersey. A large share of the House Republicans considered more moderate also represent districts in this bloc.

The core of Democratic strength in the House is the “hi-hi” districts that combine elevated levels of both racial minorities and college-educated whites. Democrats hold 98 of the 113 House seats in this category. Many of the party’s most visible members represent seats fitting this description, including former Speaker Nancy Pelosi; the current House Democratic leader, Hakeem Jeffries; former House Intelligence Committee chair Adam Schiff; and Alexandria Ocasio-Cortez. These are also the strongholds for Democrats representing what Pastor calls the places where “diversity is increasing the most”: inner suburbs in major metropolitan areas. Among the members representing those sorts of constituencies are Lucy McBath of Georgia, Abigail Spanberger of Virginia, and Ro Khanna and Zoe Lofgren of California.

Though Democrats are not as dependent on any single quadrant as Republicans are on the low-diversity, low-education districts, each party over the past decade has been forced to retreat into its demographic citadel. As Drutman notes, that’s the result of a succession of wave elections that has culled many of the members from each side who had earlier survived in districts demographically and economically trending toward the other.

The first victims were the so-called blue-dog Democrats, who had held on to “lo-lo” districts long after they flipped to mostly backing Republican presidential candidates. Those Democrats from rural and small-town areas, many of them in the South, had started declining in the ’90s. Still, as late as 2009, during the first Congress of Barack Obama’s presidency, Republicans held only 20 more seats than Democrats did in the “lo-lo” quadrant. Democrats from those districts composed almost as large a share of the total party caucus in that Congress as did members from the “hi-hi” districts.

But the 2010 Tea Party landslide virtually exterminated the blue dogs. After that election, the GOP edge in the lo-lo districts exploded to 90 seats; it reached 125 seats after redistricting and further GOP gains in the 2014 election. Today the districts low in diversity and white-education levels account for just one in 10 of all House Democratic seats, and the “hi-hi” seats make up nearly half. The seats low in diversity and high in white education (about one-fourth) and those high in diversity and low in white education (about one-sixth), provide the remainder.

For House Republicans, losses in the 2018 midterms represented the demographic bookend to their blue-collar, small-town gains in 2010. In 2018, Democrats, powered by white-collar antipathy toward Trump, swept away a long list of House Republicans who had held on to well-educated suburban districts that had been trending away from the GOP at the presidential level since Bill Clinton’s era.

Today, districts with a higher share of white college graduates than the nation overall account for less than one-fourth of all GOP seats, down from one-third in 2009. The heavily blue-collar “lo-lo” districts have grown from just over half of the GOP conference in 2009 to their current level of nearly two-thirds. (The share of Republicans in seats with more minorities and fewer white college graduates than average has remained constant since 2009, at about one in seven.)

Each party is pushing an economic agenda that collides with the immediate economic interests of a large portion of its voters. “The party leadership has not caught up with the coalitions,” says former Representative Tom Davis, who served as chair of the National Republican Congressional Committee.

For years, some progressives have feared that Democrats would back away from a populist economic agenda if the party grew more reliant on affluent voters. That shift has certainly occurred, with Democrats now holding 128 of the 198 House districts where the median income exceeds the national level. But the party has continued to advocate for a redistributionist economic agenda that seeks higher taxes on upper-income adults to fund expanded social programs for working-class families, as proposed in President Joe Biden’s latest budget. The one concession to the new coalition reality is that Democrats now seek to exempt from higher taxes families earning up to $400,000—a level that earlier generations of Democrats probably would have considered much too high.

Republicans face more dissonance between their reconfigured coalition and their agenda. Though the GOP holds 152 of the 237 districts where the median income trails the national level, the party continues to champion big cuts in domestic social programs that benefit low-income families while pushing tax cuts that mostly flow toward the wealthy and corporations. As former Democratic Representative David Price, now a visiting fellow at Duke University’s Sanford School of Public Policy, says, there “is a pretty profound disconnect” between the GOP’s economic agenda and “the economic deprivation and what you would think would be a pretty clear set of needs” of the districts the party represents.

Each of these seeming contradictions underscores how cultural affinity has displaced economic interest as the most powerful glue binding each side’s coalition. Republicans like Davis lament that their party can no longer win culturally liberal suburban voters by warning that Democrats will raise their taxes; Democrats like Price express frustration that their party can’t win culturally conservative rural voters by portraying Republicans as threats to Social Security and Medicare.

The advantage for Republicans in this new alignment is that there are still many more seats where whites exceed their share of the national population than seats with more minorities than average. Likewise, the number of seats with fewer white college graduates than the nation overall exceeds the number with more.

That probably gives Republicans a slight advantage in the struggle for House control over the next few years. Of the 22 House seats that the nonpartisan Cook Political Report currently rates as toss-ups or leaning toward the other party in 2024, for instance, 14 have fewer minorities than average and 12 have fewer white college graduates. “On the wedge issues, a lot of the swing districts look a little bit more like Republican districts than Democratic districts,” says Drutman, whose own recent analysis of House districts used an academic polling project to assess attitudes in all 435 seats.

But as Pastor points out, Republicans are growing more dependent on those heavily white and non-college-educated districts as society overall is growing more diverse and better educated, especially in younger generations. “It’s hard to see how the Republicans can grow their coalition,” Pastor told me, with the militant culture-war messages they are using “to cement their current coalition.”

Davis, the former NRCC chair, also worries that the GOP is relying too much on squeezing bigger margins from shrinking groups. The way out of that trap, he argues, is for Republicans to continue advancing from the beachheads they have established in recent years among more culturally conservative voters of color, especially Latino men.

But Republicans may struggle to make sufficient gains with those voters to significantly shift the balance of power in the House: Though the party last year improved among Latinos in Florida, the results in Arizona, Nevada, and even Texas showed the GOP still facing substantial barriers. The Trump-era GOP also continues to face towering resistance in well-educated areas, which limits any potential recovery there: In 2020, Biden, stunningly, carried more than four-fifths of the House districts where the share of college-educated white adults exceeds the national level. Conversely, despite Biden’s emphasis on delivering tangible economic benefits to working families, Democrats still faced enormous deficits with blue-collar white voters in the midterms. With many of its most vulnerable members defending such working-class terrain, Democrats could lose even more of those seats in 2024.

Constrained by these offsetting dynamics, neither party appears well positioned to break into a clear lead in the House. The two sides look more likely to remain trapped in a grinding form of electoral trench warfare in which they control competing bands of districts that are almost equal in number, but utterly antithetical in their demographic, economic, and ideological profile.