Revisiting What Happened in the 2018 Election

  1. Turnout increased dramatically compared to past midterms, and the composition of the 2018 electorate resembled recent Presidential electorates much more than recent midterms. Young voters and voters of color, particularly Latinx voters, were a substantially larger share of the electorate than in past midterms. White non-college voters and people we’ve historically modeled as Republican supporters were a smaller share. The 2018 electorate was similar to 2016, with the exception of age: midterm electorates are older than Presidential electorates generally speaking, and 2018 ended up somewhere between 2016 and 2014 in this regard.
  2. Comparing the 2018 Congressional results to the 2016 Presidential election, Democrats gained about 5 points in margin[2], but Democratic gains were uneven across different parts of the electorate. We saw the biggest gains among young white voters, white college voters, and people we’ve historically modeled as neither Democratic nor Republican — these aren’t exactly “Independents” but we think this is a meaningful group.
  3. Democratic gains were uneven across geography too, both at the Congressional level and in statewide elections. There has been a lot of attention paid to the Democratic victories in suburban areas, but we find that Democratic gains were actually largest in rural areas. These gains weren’t enough to get over 50% and win seats in many rural districts, so they have escaped much of the mainstream election analysis to this point. These changes are nonetheless important, particularly because they were large in many of the midwest battleground states that will no doubt be important in 2020.
  4. Compared to 2010 and 2014, 2018 saw (a) less Presidential dropoff (people who voted in the Presidential election and didn’t vote in the midterm), and (b) more midterm surge voters (people who didn’t vote in the last Presidential but did vote this time). Voting patterns for all of these groups show more Democratic enthusiasm and support than past years.
  5. Thinking about the change from 2016 to 2018, it is clear that both mobilization and persuasion were critically important in producing this scale of victory for Democrats. When it comes to turnout, the composition of the electorate roughly “broke even” with 2016, much different than the past two midterms. But “breaking even” doesn’t explain the amount and geography of gains that Democrats saw. A large portion of gains came from people who voted in both elections, switching from supporting Trump in 2016 to supporting Democrats in 2018. We show some of the math behind this, including how that conclusion changes in different areas of the country.
  6. Looking ahead to 2020, it is reasonable to expect another historic level of turnout, perhaps approaching 160 million votes or more. It is not safe, however, to assume that Democratic gains from 2016 to 2018 will hold. Republican gains in 2010 and 2014 bounced back to Democrats 2 years later (at least in the national popular vote in 2016), and Democrats should be aware this is a distinct possibility going into 2020 as well.

Composition of the Electorate and Voter Turnout

The composition of the 2018 electorate resembled recent Presidential elections more than recent midterms.
Turnout rates by age, across selected recent elections.

Vote Choice

The major turnout surge in 2018 was only part of the story. Democrats saw gains across many different areas of the country, due to both turnout and changing vote choice, i.e., people switching from voting for Donald Trump in 2016 to voting for Democrats in 2018. We will examine turnout versus vote choice more explicitly later on, but first this section lays out baseline data for how different groups voted in recent elections.

Democrats gained 5 points in margin nationally, but gains were uneven across demographic groups.


Democratic gains were also geographically uneven across the country. In our view, these trends have been fairly widely mischaracterized[4]. Most people are probably familiar with the large-scale rural/suburban/urban story from 2016. Despite rural areas being more Republican even before this election, the change from 2012 to 2016 was dramatic: rural areas became even more Republican, suburban areas became more Democratic, and urban areas largely stayed the same, with small shifts towards Democrats:

Rural America shifted towards Republicans from 2012 to 2016.
Despite media narratives to the contrary, rural American bounced back towards Democrats in 2018.
The urban/suburban/rural trends, shown more explicitly.

Presidential Dropoff and Midterm Surge

Traditional election analysis, including the earlier sections of this post, deal with fairly standard sets of group-level aggregate data. Who did Latinx voters support (as a group), and how did Precinct X vote (as a group)? Using individual-level voter registration data, collected over time, opens up the possibility for different groups that are defined by their recorded behavior.

  1. People who voted both times
  2. People who voted neither time
  3. People who voted in 2016 but not 2018 (Presidential dropoff voters)
  4. People who didn’t vote in 2016 but did vote in 2018 (midterm surge voters)
Higher turnout was associated with relatively low voter dropoff from 2016, and a large number of new voters.

Putting It Together: Different Electorate and Different Vote Choice

As different years bring different election results, many people have debated the extent to which these changes are driven by (a) differential turnout or (b) changing vote choice.

  1. President to midterm dropoff voters: how much loss was due to Democrats who voted in 2012 but dropped off and didn’t vote in 2014?
  2. New, midterm surge voters: how many new votes did Republicans gain due to new voters who showed up in 2014 but not in 2012?
  3. Changing vote choice among people who voted both times: did this happen, and to what extent?
Decomposing the change in total outcome (margin) from 2012 to 2014. In this case, the change was likely mostly due to differential turnout.
Decomposing the change in total outcome (margin) from 2016 to 2018. Turnout was important in essentially breaking even with 2016, but Democratic gains were also largely driven by voters who voted for Trump in 2016 and voted Democratic in 2018.
Decomposing the change in total outcome (margin) from 2016 to 2018, for different statewide and Congressional elections. Dynamics changed from place to place, but overall, many of the places that saw big Democratic gains had a large component of vote choice, i.e., Trump to 2018 Democratic voters. Geographies are sized by how competitive they were in 2018[10].

Looking Ahead to 2020

This analysis has many implications for the 2020 Presidential election, frankly too many to be covered in detail in this post. We’ll briefly focus on three topline takeaways here.

Expect a historic number of votes in 2020.
Decomposing the change in total outcome (margin), for the last two Presidential swings. States are sized by how competitive they were in the latter election.
Republican gains in the past two midterms swung back towards Democrats in the following Presidential election. The diagonal line shows 100% “bounce-back” from one election to the next. In both cases (key groups on the left, a random sample of 10,000 individual-level estimates on the right), there was a substantial swing back.

Appendix: Notes on Statistical Methods

We published our preliminary estimates the week after the election, and since then have been collecting various new pieces of data to verify and update what we saw back then. Looking back on the preliminary data and analysis, we think that the estimates were very accurate in many cases and slightly off in some other cases. Substantively, our judgment is that the analysis holds up, with some important caveats.

Appendix: Decomposing Changes in Turnout and Vote Choice

The calculations described earlier to decompose the margin change are shown below. One complication is third party voting, which was higher in 2016 than other years. Different versions of these calculations were done, by excluding third party voters or projecting their two-party vote share. Results remained the same under these different sets of calculations.

Calculations for margin decomposition, 2012 to 2014 (top) and 2016 to 2018 (bottom).



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