On Sabato’s Crystal Ball, Professor Alan I. Abramowitz writes that it is incumbency, not gerrymandering that is the reason the Democrats are unlikely to win a U.S. House majority, even with a Clinton landslide. FairVote agrees, to a point. Both gerrymandering and incumbency play a role in denying the Democrats a majority in the U.S. House even when they win a majority of votes.
While the Democrats would win more seats if there was no gerrymandering or incumbents, they would not win a proportional number of seats.
Academic analyses indicate the gerrymandering accounts for little of the bias in the U.S. House (which currently favors Republicans, but has, in the past, favored Democrats). FairVote’s modelling shows that if every seat was open (i.e. there were no incumbents), Democrats would need to win around 52.8% of the national vote to win a majority (218 seats to 217) in the U.S. House.
A larger theme is the problem of districting in an increasingly geographically divided America. Decades ago, Republican- and Democratic-leaning voters were more evenly distributed throughout the country, in rural, suburban and urban areas. Today, Americans increasingly live in communities inhabited by people with similar perspectives and worldviews to their own, and have less contact with those on the other side of the ideological divide. In this America, it is very difficult to draw competitive districts – at least ones that don’t look completely gerrymandered – because each competitive district would need to take in a little bit of a city and larger parts of suburban or rural areas.