The Daily Kos has completed its yeoman’s work of determining how each congressional district voted in the presidential race. This is harder than it sounds: Because we conduct elections at the county level and congressional districts sprawl around states in whatever way best ensures partisan control, matching up those two sets of data requires a lot of close attention being paid to random precincts.

Doing so, though, allows us to get a more complete picture of the extent to which U.S. voters split their tickets in 2016. In other words, we can now see where districts voted for a member of one party for Congress and the presidential candidate of the other party.

Over time, the number of places that have done that has declined. We looked at this in 2014, using data from Polidata and past Daily Kos analysis. This allowed us to see how split-ticket voting has evolved since 1992.

Consider this chart, contrasting congressional and presidential votes this year.

If every congressional district were won by members of the House and presidential candidates of the same party and margin, every dot would fall on that yellow diagonal line. A lot come close! Dots above the line saw a wider margin for the Republican in the congressional race; those below, a wider margin for the Democrat. The region that’s blue indicates districts where the Democrat won both races. The red region shows the Republican winning both.

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Notice that most of the dots fall into one of those regions. Most voters, in other words, voted for the same party to hold the House seat and the presidency. But not all. The dots in the upper left and lower right quadrants split their tickets.

First, let’s look at how that’s evolved over time. Notice how the dots are increasingly clustered around the yellow line as we look back at election results.

For off-year elections, we compare congressional results with the preceding presidential election. So notice what happens in 2010, for example: More dots above the yellow line as Republicans fared much better in congressional races.

It can be hard to see precisely how many districts split their votes in that animation, though. So here’s a simple graph of ticket-splitting in each congressional election since Bill Clinton won in 1992.

You see far fewer light-colored bar areas this year than 20 years ago. Not an all-time low in our data set, but close. (The low was 2012.) This isn’t necessarily all because of split-ticket voting, mind you. Some voters may have gone out to vote for the member of Congress that they liked, but then skipped voting in the presidential race. But the effect is the same: a district that’s a dichotomy.

So where were those split districts this year? Here.

(An earlier version of this map didn’t render properly. It has been updated.)

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Hillary Clinton picked up districts in California, Washington and New York won by Republican members of the House, though she would have won those states anyway. Donald Trump picked up districts in Minnesota, Iowa and Wisconsin — in the region that powered his surprise electoral victory. Clinton overperformed in cities in Texas, narrowing the margin there relative to how then-President Obama did in 2012, but she didn’t come close to winning the state. (Although the final margin there was narrower than in Iowa.) That’s the big picture of the 2016 election: Clinton doing better in places with a lot of votes, leading her to a popular vote victory. But Trump doing better where it matters.

Split ticket voting doesn’t happen very often any more. In 2016, though, where it happened was important — to Clinton’s detriment.

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