Dr. Borick pointed out that while state-level polls had widely misfired in 2016, they held steady in the 2018 midterms. This led him to conclude that people’s views on Mr. Trump may be particularly difficult to measure.

“In the end, like so many Trump-related things, there may be different rules when polling an election with him on the ballot,” Dr. Borick said. “I’m a quantifiable type of human being; I want to see evidence. And I only have two elections with Donald Trump in them — but both seem to be behaving in ways that others don’t behave.”

Analyzing pre-election polls alongside exit polls is like comparing apples to apples — if one batch is rotten, the other probably is, too. But the exit polls can still provide a few clues as to what pre-election polls might have missed.

At the top of that list is Mr. Trump’s strength among college-educated white voters, particularly men. According to the exit polls, the candidates split white college graduates evenly — after an election season in which almost every major poll of the country and of battleground states had shown Mr. Biden ahead with white degreeholders.