A majority of the GOP gains since then have come from the Democrats’ near-total collapse in one set of districts: the largely blue-collar places in which the white share of the population exceeds the national average, and the portion of whites with at least a four-year college degree is less that the national average. While Republicans held a 20-seat lead in the districts that fit that description in the 111th Congress, the party has swelled that advantage to a crushing 125 seats today. That 105-seat expansion of the GOP margin in these districts by itself accounts for about three-quarters of the 136-seat swing from the Democrats’ 77-seat majority in 2009 to the 59-seat majority Republicans enjoy in the Congress convening now.

The GOP dominance in these predominantly white working-class districts underscores the structural challenge facing Democrats: While the party has repeatedly captured the White House despite big deficits among the working-class white voters who once anchored its electoral coalition, these results show how difficult it will be to recapture the House without improving on that performance. “The question is: Are we at rock bottom here?” says Tom Bonier, CEO of the Democratic voter targeting firm TargetSmart Communications.

These trends present Republicans with a mirror-image challenge. The vast majority of their House members can thrive without devising an agenda on issues—such as immigration reform—that attract the minority voters whose growing numbers nationally have helped Democrats win the popular vote in five of the past six presidential elections. “When you can go out screaming ‘amnesty’ and not get any pushback in your districts, you are more prone to scream ‘amnesty,’ ” says veteran GOP pollster Whit Ayres. “It leads to an attitude of: ‘problem, what problem?’ “