“What we saw in 2012 and 2014 with the demographic realities in congressional districts around the country is now manifesting itself through the Electoral College as well,” said Jesse Ferguson, a top communications strategist for Clinton’s campaign, who previously held the same role for the Democratic Congressional Campaign Committee. “Democrats still have a popular-vote advantage in this country, but when you allocate political strength by any measure of geography—and not demography—it is not advantageous to Democrats. That started … in the House, and via the Electoral College it was true in 2016 [in the presidential race].”

The Four Quadrants

To understand the impact of demography on the House, The Atlantic examined congressional district-level data from the Census Bureau’s 2015 American Community Survey. (The ACS data for 2015 does not take into account the recent court-ordered redistricting in North Carolina, Florida, and Virginia, so there may be some variation from the numbers reported here in the revised districts in those states.)

The contrast between the two parties’ demographic bases becomes most apparent by segmenting House districts based on two factors: whether the share of their non-white population exceeds or trails the national average of 38.5 percent, and whether the share of their white population with at least a four-year college degree exceeds or trails the national average of 34.2 percent. The numbers reflect the results for each district’s entire population. The analysis focused on the education level among whites, and not the entire population, because education is a more significant dividing line in the political behavior of whites than of minorities.

As we’ve written before, sorting congressional districts by the two variables of race and education produces what we call the four quadrants of Congress: districts with high levels of racial diversity and high levels of white education (what we call “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 low levels of white education (“lo-lo districts”).

Hi-Hi Districts

The center of the modern Democratic House caucus is the hi-hi districts that exceed the national average in both share of racial minorities and share of white college graduates: Democrats hold fully 87 of the 108 districts that fit that description. That list divides between minority Democrats in districts with large non-white populations—such as Georgia’s John Lewis, Texas’s Joaquin Castro, and Illinois’s Bobby Rush—and primarily white members representing diverse but more affluent districts, such as Nancy Pelosi and Anna Eshoo of California, Diana DeGette of Colorado, and Jim Himes of Connecticut.

Hi-Lo Districts

Democrats also hold a less lopsided 44-to-24-seat advantage in districts that are high in racial diversity but are below the national average in white college graduates. That roster tilts heavily toward minority Democrats, such as Linda Sanchez and Lucille Roybal-Allard in California, José Serrano in New York, and Raúl Grijalva in Arizona. But it also includes some white representatives from diverse but middle- and working-class areas, like Dina Titus in Nevada.

Lo-Hi Districts

In turn, Republicans hold a decisive lead in districts where whites exceed their presence in the national population. The GOP leads by a narrow 44 to 39 margin in the lo-hi districts, where there are relatively fewer minorities but more white college graduates than the national average. This is the most closely contested quadrant. On the Republican side, it includes members representing affluent suburbs, such as Patrick Meehan in Pennsylvania, Kevin Yoder in Kansas, and Barbara Comstock in Virginia. The mostly white Democrats in this lo-hi group tend to represent urban centers or inner suburbs, too, such as John Yarmuth of Kentucky, Earl Blumenauer of Oregon, and Jared Polis of Colorado.

Lo-Lo Districts

The foundation of the GOP majority is the lo-lo districts, where the shares of minorities and whites with a college degree both trail the national average. In those districts with large populations of blue-collar whites, Republicans now hold a lead that is so lopsided as to be almost incomprehensible: They control 152 of these seats, compared with just 24 for Democrats. This quadrant houses almost all of the Republicans representing rural places—such as Kentucky’s Hal Rogers, Missouri’s Jason Smith, and Iowa’s Steve King—as well as the GOP’s growing contingent of members representing smaller metro areas, such as Bill Shuster of Pennsylvania and Jim Jordan of Ohio. It’s also the last redoubt for the few Democrats remaining in heavily rural districts, such as Minnesota’s Collin Peterson, or those representing largely blue-collar smaller cities, such as Ohio’s Marcy Kaptur and Tim Ryan or Pennsylvania’s Martin Cartwright.

Just as large margins in those rural and small-town communities powered Trump’s victory, so, too, have the gains there keyed the Republican House takeover. Compared with the 111th Congress from early 2009 to early 2011—when Democrats last controlled the majority—the Democratic Party has actually widened its advantage in the districts high in both diversity and college-educated whites (from 50 seats then to 66 now). Since then, Democrats have lost ground modestly in the high-diversity districts with fewer-than-average white college graduates (from a 28-seat advantage to a 20-seat edge now). The party has also skidded somewhat more sharply in the districts with low diversity and large numbers of college-educated whites (from an advantage of 19 seats then to a deficit of five now).