Daily Kos Elections recently completed calculating the 2016 presidential election results by congressional district. With ticket-splitting rates at historic lows, and presidential results highly correlated with congressional results, these numbers serve as a strong predictor of future House election outcomes. Accordingly, the districts that saw Hillary Clinton’s margin improve the most compared to Barack Obama’s 2012 margin could point toward future trends in House races. Below we’ll take a look at the 25 districts that swung hardest toward Clinton, all of which moved by at least 13 points.
As shown on the map above (see here for a larger image), the vast majority of these 25 seats are heavily suburban, well-educated, diverse, and concentrated in Sun Belt states like California and Texas. Twenty of them ranked in the top fifth of all districts by the share of adults with a college degree, and college-educated white voters in particular voted much more strongly Democratic than whites without a degree did in 2016 when compared to past elections. Two of the remaining seats were majority Latino, and the last three were in Utah, where socially conservative Mormon voters who usually lean heavily Republican were exceptionally hostile to Trump.
Overall, Clinton won 15 of these districts, although six of those were already dark blue. Trump won the other 10, including four of them by double digits. However, six districts flipped from Romney to Clinton, while another six saw the GOP margin shrink from greater than 20 percent to less than 10 points. Congressional Republicans hold 17 of these seats and Democrats just 8. However, all of those House Republicans performed much better than Trump did, and only two prevailed by less than 10 points. However, many of their seats could be particularly vulnerable if the 2016 presidential trend filters further downballot, or if they retire.
A prefatory note on Utah is necessary. As a Mormon, Mitt Romney was unusually popular in the Beehive State for a Republican, while Donald Trump was even more uniquely despised by Republican voters there. Many of them abandoned Trump for conservative independent Evan McMullin, himself a Mormon, magnifying the state’s swing away from Republicans in 2016. In fact, McMullin even came in second over Clinton with 24.5 percent in the Provo-based 3rd District. That seat saw the biggest drop in the Republican margin over Democrats of any seat, with Trump’s 25 percent margin a giant 35 percent smaller than Romney’s 59-point victory in 2012.