Daily Kos Elections has combined our calculations of the results of the presidential elections from 2008 to 2016 for every congressional district with our unique hexmap that renders each district the same size, to show which party’s presidential candidate won each district across all three elections. You can see how every district has performed in the map at the top of this post (see here for a larger image), but there’s much more below.
These statistics are so important because the presidential results are very strongly correlated with how congressional candidates from each party perform in a given district. Widespread GOP gerrymandering is the chief reason why congressional lines favor Republicans nationally, but there are many districts that nevertheless flipped between the parties across these presidential elections.
Even though Democrats won the popular vote in all three presidential races, Republican nominees won a majority of all congressional districts twice during that time: Donald Trump carried 228 districts in 2016 and Mitt Romney won 220 seats in 2012, out of 435 total. Barack Obama only captured a majority of districts in his 2008 landslide, when he won 242. Despite that GOP advantage, only 184 districts voted Republican in all three of those elections.
Consequently, if some of these districts revert to earlier patterns in the 2018 midterms, Democrats may be able to capitalize. Our maps below detail just how consistently partisan most of the districts held by each party are, but they also show that the GOP holds a large number of seats that have voted Democratic in at least one of the past three presidential races. Those seats could post a particular danger to Republicans if 2018 turns into a true Democratic wave election.
The map below shows all 195 Democratic-held seats in the House, assigning all vacant seats to the party that last held them. As you can see, only 13 of them, or 7 percent, did not back the Democratic presidential nominee at least once in the last three elections; indeed, all 13 voted for Trump. Reflective of their minority status, Democrats hold just four seats that voted for the GOP presidential candidate in each of the last three elections.
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This next map shows those 13 Democratic seats in isolation in order to give you an idea of just how few Democrats hold seats that truly lean against their party. This points to one silver lining of being in the minority: There simply aren't many good targets for the GOP, especially with 2018 shaping up to be a Democratic-favoring year.
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By contrast, 60 Republicans hold seats that backed at least one Democratic nominee over the last three elections as shown below—fully 25 percent of their current caucus of 240. Furthermore, 12 of them hold districts that supported the Democratic nominee in all three elections, making those seats excellent Democratic targets, while another 16 favored the Democratic nominee twice.
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Filtering out the Republicans who hold consistently red seats, as we do below, allows us to better see those 60 seats that went Democratic in at least one presidential race. These seats aren’t an exhaustive list of Democratic targets in 2018, and some of them may in fact be secure for their incumbents. But as we noted, there’s such a strong degree of correlation between presidential and House outcomes that these districts are likely to include most of the 23 races Democrats need to flip to gain a majority.
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Note: All presidential election results are calculated according to congressional district boundaries in effect for the 2018 elections.
