What Democrats could lose with their left turn

The experiment’s procedure was simple. A random half of participants read a news snippet illustrating the leftward shift, while the other half read about unrelated topics, such as the schedule of election dates. The news item was a few sentences that included policies discussed by the candidates: decriminalizing unauthorized border crossings; expanding undocumented immigrants’ access to government services; replacing private health insurance with a government-run system; and establishing free public college for all children from working-class families. The content was drawn directly from real news coverage.

Both sets of respondents then indicated how they planned to vote in 2020 (whether for President Trump or the eventual Democratic nominee), how strongly they were considering voting Democratic, and how motivated they felt to turn out and vote for or against the Democratic nominee. Because of the random assignment — with some reading about the policy positions and others reading innocuous, unrelated information — the difference in responses between the groups can be attributed to the effect of reading about the leftward shift.

When deciding between Mr. Trump and the Democratic nominee, voters in the middle — the independents who could ultimately tilt things in Mr. Trump’s favor — became six percentage points less likely to vote Democratic after reading about the leftward turn compared with the independents who had read the innocuous content.