… There is also strong evidence that most traditional public opinion surveys inadvertently hide a segment of Trump’s supporters. Many voters are reluctant to admit to a live interviewer that they back a candidate who has adopted such divisive positions.
In matchups between Trump and Hillary Clinton, Trump does much better in polls conducted online, in which respondents click their answers on a computer screen, rather than in person-to-person landline and cellphone surveys. …
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. … Needless to say, Trump has expressed confrontational views on a number of fronts. CONT.
Thomas B. Edsall, New York Times