The battleground in the House is really big -- and that makes life hard for Republicans

Democrats’ ceiling is sensitive to these minor changes in the political environment because there are a glut of districts that are somewhere between 10- and 20- percentage points more Republican-leaning than the country as a whole. Many of these districts were gerrymandered to be “safe” for Republican candidates. And in a medium-sized wave — say, one that featured a Democratic lead on the generic ballot of 6 to 7 percentage points — they probably would be safe. But once Democrats get up to about an 8- or 9-point lead instead, they’re really bumping up against the walls of these gerrymandered districts, and they may encounter incumbents who are underfunded and otherwise not-well-prepared for the challenge. In that sense, the Washington Post’s analysis was right: A relatively minor shift back toward Republicans, especially in conservative areas, could have really limited the Democrats’ upside potential. It was just mistimed; the shift that occurred toward Republicans in early October is no longer really evident in the polls now.1 Instead, Democratic candidates for Congress continue to poll well in some Trump-friendly districts as well as those that voted for Hillary Clinton for president.

Our Classic model incorporates “fundamentals” in addition to the polls — most importantly, including fundraising. And it shows the number of competitive districts generally having increased over time as Democrats’ fundraising numbers get better and better, especially in Republican-leaning areas where you’d ordinarily expect the incumbent to have a heavy fundraising advantage. In particular, there’s a spike in the number of competitive districts in the Classic forecast on or about Oct. 15, when third-quarter fundraising totals were reported to the FEC and incorporated into the model. The Classic model now shows around 110 competitive districts, the vast majority of which are currently held by Republicans. Since Democrats only need to win 23 of these to win the House — potentially plus a few extra to cover a couple of districts of their own they might lose — you can see why it’s become pretty bullish on Democrats’ chances.