The first map below presents the 2016 presidential election margin in each state as a frame of reference (see our spreadsheet for results by state). Clinton won 20 states and Trump 30, but Trump only captured Florida, Michigan, Pennsylvania, and Wisconsin by roughly 1 percent or less, and Arizona and North Carolina by less than 4 points each.
By contrast, this second map below shows the presidential election margin just in each state’s median congressional district. This map reveals that Trump won the median seat in 32 states, including even in Minnesota and Virginia, which Clinton carried at the statewide level. And Trump also easily prevailed in the median district in Michigan, North Carolina, Pennsylvania, and Wisconsin despite only narrowly defeating Clinton statewide there.
If you “subtract” the first map from the second map, what you wind up with is the map at the very top of this post, which shows the advantage in the median district. Trump obtained a median seat advantage of at least 5 percent in 18 states and 10 percent or more in six states. Missouri offered the biggest median seat advantage in the country, with Trump carrying its median district by a staggering 15 percent more than his statewide margin.
On the other hand, Democrats enjoyed a median seat advantage of 5 points or greater in just three states, with California having the largest advantage of 7 percent. That, however, barely even cracks the top 15 states overall. Just 20 states had a median seat advantage of less than 2 points for either party, but seven of those states only have a single district. Another five in this category have just two districts, so as a practical matter, states this small don’t even really have a median seat worth analyzing.
It’s also worth looking at how each state’s median seat advantage changed between 2016 and 2012, which is what you see in the map below. This tells us whether each state’s advantage shifted in a more Democratic or Republican direction over the last four years, which could in turn be a sign that a gerrymander has become weaker or stronger over time.
Fortunately for Democrats, Republican median seat advantages shrunk in several states where the GOP had a significant edge in 2012. That was particularly so in the Sun Belt, where Clinton dramatically improved on Obama’s deficit in red states like Texas and Georgia, indicating that Democrats could gain districts that Republicans had intended to be safely red if those seats continue trending Democratic overall. But on the other hand, the median seat advantage did grow more Republican in a few key swing states such as Minnesota, Virginia, and Wisconsin.
Most importantly, the GOP’s national median seat advantage stayed almost exactly the same. As we noted above, the national median gave Trump a 5.5 percent advantage; four years ago, it favored Mitt Romney by 5.4 points. In short, this means that while Republican gerrymanders might be weakening in some specific states like Texas, their efficacy nationally is as strong as ever. (You can find every state’s median congressional seat and the resulting partisan advantage score comparing it to the statewide result in this spreadsheet, or in the chart embedded at the bottom of this post.)
Now you might be wondering, just how much of these median seat advantages actually comes from gerrymandering as opposed to the geographic clustering of voters from one party. In other words, do these advantages come about because Democrats tend to live in cities that vote, say, 80 percent Democratic while Republicans are more evenly spread out in rural areas and suburbs that might only vote 60 percent Republican? That’s a surprisingly difficult question to tackle, but it’s one that Daily Kos Elections has worked extensively to address.
The map below (known as a cartogram) depicts each congressional district as equally sized. The map itself shows what we call the “partisan intent” behind each state’s congressional map, regardless of whether those maps were drawn by a legislature, a commission, or a court. (Even ostensibly non-partisan bodies like courts and commissions can wind up intentionally favoring one party’s preferred maps over the other’s.) As you can see, maps drawn to favor Republicans covered 55 percent of districts nationwide, while those intended to help Democrats amounted to only 10 percent of all seats.
Several of the states with large Republican median seat advantages like Michigan, North Carolina, Ohio, Pennsylvania, and Wisconsin saw extremely aggressive Republican gerrymanders that undoubtedly contributed considerably to the GOP’s edge. Those gerrymanders played a decisive role in helping Mitt Romney carry the median district four years ago in all those states—even though he lost all but one of them (and only won North Carolina narrowly).
But gerrymandering does not explain the median seat advantage in every state. Minnesota, for instance, had a very large 10 percent Republican median seat advantage in 2016 even though a court drew a genuinely nonpartisan map. That tells us that geographic clustering really did hamper Democrats there.
Meanwhile, Illinois was home to one of the very few aggressive Democratic gerrymanders following the 2010 census, but Democratic cartographers there managed to come up with only a 1 percent median seat advantage in Team Blue’s favor. That’s another indication of geography working against Democrats. It’s also a reminder that the party drawing a gerrymander doesn’t always try to make all of their intended districts as lopsided as possible; instead, they often spread their voters out to win as many districts as they can. As such, median seat advantages only tell part of the story about how gerrymandered states are, particularly when those states already lean heavily toward one party.
To determine how much blame gerrymandering and geography bear for America’s congressional districts overall having a systematic Republican advantage, Daily Kos Elections has proposed nonpartisan maps for every state. We’ve calculated the presidential results for these hypothetical districts, and doing so strongly suggested that gerrymandering bears far more blame than geographic clustering in 2012. In the coming weeks, we’ll recreate this analysis using last year’s results, which will allow us to fully investigate just how large of a role gerrymandering played in creating 2016’s median seat advantages for the GOP.
Median Congressional Districts (2012 & 2016)
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