From “Rumblings from Trump’s base could shape Democrats’ choice for 2020” by Ronald Browstein at CNN Politics:
Detailed new research by the Democratic voter-targeting firm Catalist found that the party’s big gains in the 2018 congressional election were fueled not only by unusually high turnout among voters sympathetic to the party, but also by larger-than-expected defections from the GOP among voters who had backed Trump two years earlier.Those findings offer potentially critical evidence as Democrats are debating the best approach to beating Trump in 2020. On one side are progressive activists who say the party should prioritize mobilizing nonvoters, particularly young people and minorities, with an unabashedly liberal agenda. On the other are centrists who say Democrats can’t tilt so far left on issues such as single-payer health care and the Green New Deal that they alienate swing voters who backed Trump in 2016 but may be open to reconsidering now.
“The number one thing I would say is winning elections isn’t just about mobilization,” said Yair Ghitza, Catalist’s chief scientist, in an interview. “I do think that’s something some people argue, and it’s gained a bit of traction. What I try to point out here is that mobilization is incredibly important. But the idea that there are literally no swing voters left, is, I think, a misreading of a lot of the data that’s out there.”
In 2018, Catalist calculated, Democrats won the total popular vote in House elections by 7 seven percentage points (after making projections for uncontested races). That was a gain of about 5 percentage points from Hillary Clinton’s popular-vote margin over Trump in 2016.That change derived from three big sources: who left the electorate between 2016 and 2018, who entered it and the changing preferences of voters who participated both times.
Brownstein explains that “The falloff from voters who participate in the presidential election but then sit out the next midterm has become a huge problem for Democrats as their coalition has grown more dependent on young people and minorities; both of those groups turn out much more reliably in presidential than in midterm elections.” Thus “considerably more Democratic than Republican voters typically stay home in the off-year election. That falloff was so severe from then-President Barack Obama’s re-election victory in 2012 to the GOP sweep in 2014, for instance, that Ghitza calculates it cost Democrats fully 6 points in their share of the total vote.”
However, “because of the turnout gains among key party constituencies, that drop-off was much less of a problem” and, “in 2018, only about 27% of 2016 voters sat out, Catalist found.” In addition, “Republicans also suffered a drop-off, particularly among non-college whites and rural whites, two of Trump’s key groups. Minorities, who usually slip as a share of the midterm vote, represented almost exactly as much of the vote in 2018 as they had in 2016. And while young people still declined as a share of the electorate in 2018, they did not do so nearly as severely as in the previous two midterm elections.” Moreover,
The overall result was voters who sat out the 2018 midterms after voting in 2016 cost the Democrats a manageable 2 percentage points in the total vote last year, only about one-third of their crushing decline in 2014.And last year, Democrats offset that loss through the other major factor that shifted the electorate’s composition: new voters. Catalist found that about 13% of the 2018 voters, some 14 million people, had not voted in 2016. That was a significantly bigger surge of new voters than in 2010 and 2014, when about 9% of the electorate had not participated in the previous presidential election.
And while the new voters had favored Republicans by 2 percentage points in 2010 and by a solid 7 percentage points in 2014, they provided Democrats a resounding advantage of 21 percentage points last year.In all, Catalist calculated, new voters swelled the Democrats’ total share of the 2018 vote by about 2.6 percentage points. When combined with their loss of around 2 percentage points from 2016 voters who sat out 2018, that meant changes in the electorate’s composition contributed about half a percentage point to their overall vote gain from the presidential election to the midterm elections. That was a vast improvement from the midterm elections under Obama, when Democrats were hurt by the composition of both the drop-off and new voters.
In all, “nearly 90% of the Democrats’ increase in their total vote from 2016 to 2018 came from switches among the roughly 99 million people who participated in both elections…Vote switching, as opposed to shifts in the electorate’s composition, accounted for about three-fourths or more of the Democrats’ improvement compared with the 2016 presidential results in a wide variety of states, Catalist found. Those included their Senate victories in Pennsylvania, Michigan, Wisconsin, Ohio, Nevada and Arizona, as well as governor’s victories in Nevada, Michigan and Maine.”
The study did not calculate the impact of particular issues or events on the election results. But Brownstein quotes Ghitza’s conclusion that “it’s clear that it is best to both mobilize and persuade, and to find a message that can do both. If the Democratic candidate has a message that only appeals to certain pieces of the country, then those mobilization advantages could end up being counteracted by increasing support for Trump on the other side.”