This difference, Dropp notes, is driven largely by more educated voters — those who would be most concerned with “social desirability.”

These findings suggest that Trump will head into the general election with support from voters who are reluctant to admit their preferences to a live person in a phone survey, but who may well be inclined to cast a ballot for Trump on Election Day. . .

I asked a number of experts about the disparity between online and phone polls. All of them — Alan Abramowitz, John Sides, Michael Tesler and Lynn Vavreck, political scientists who specialize in the analysis of poll data — agreed that in the case of highly contentious issues, respondents can be more willing to express their real views anonymously, to a computer rather than to a human.