The first plausible explanation for Sanders’s higher numbers is simply that until now the polls have failed to capture the breadth of his support. It would not be the first time that he has been painfully underestimated. On the eve of the 2016 Democratic primary in Michigan, polls suggested that Sanders was trailing Hillary Clinton by some 30 percent. He went on to win, albeit narrowly. It seems to me entirely possible that, like Donald Trump, Sanders is a candidate who benefits — if that is the right verb — from what sociologists call the “shy Tory” effect: for one reason or another, voters who are reluctant to tell strangers that they support him nevertheless end up pulling the lever on Election Day.
The opposite, of course, could turn out to be true. I would be only slightly surprised if it were the case that recent state and national polls are in fact exaggerating support for Sanders. This is not incompatible with the possibility that voters who have only recently begun to take an interest in the primary election have settled on him. In fact, late decision makers surging in one direction could very easily lead to analysts drawing the wrong conclusions. One candidate can be the beneficiary of all the recent momentum in an election without ever reaching anything like a majority because so many voters have already made up their minds.