Last November saw record-setting levels of correlation between 2018’s election results for the House and the results of 2016’s presidential election in each congressional district. Put more concretely, if a district voted for Hillary Clinton, it very likely backed a Democrat for the House in the midterms; conversely, if district went for Donald Trump, it very likely sent a Republican to Congress last year.
Nevertheless, 34 members hold congressional districts after last year's elections that voted for the opposite party for president. The distribution between the two parties, however, is lopsided. As shown on the map at the top of this story (see here for a larger image and here for a cartogram with each district sized the same), these “cross-party” districts include 31 Democrats but just three Republicans.
Thanks to historic polarization between the two parties, the 2020 elections are expected to follow the trend of this decade's House elections and once again see significant straight-ticket voting with Trump leading the way for Republicans next year. Consequently, these 34 seats are likely to see some of the most heavily contested 2020 House races.
With Democrats defending their 235-seat majority, they can't afford to lose more than 17 districts if they are to remain in control of the House. And they’ll be defending difficult turf: Since Donald Trump won 228 districts to Hillary Clinton's 207, the map above illustrates where Republicans could gain a majority simply by flipping some of the 31 Democratic seats that Trump carried. Indeed, thanks to widespread Republican gerrymandering, it's possible that Republicans could once again reclaim the majority despite losing the popular vote.
To avoid that outcome, Democrats will focus much of their efforts on defending the seats mapped above. They’ll also go on offense once again: While there are only three Republicans still sitting in seats Clinton won, there are many others who occupy districts that have been trending against the GOP, particularly in affluent, well-educated suburban areas.
The two charts below detail all of the members in these cross-party districts, along with statistics on each. Both charts are sorted by the 2016 presidential margin in descending order.
