“If you want to win, you have to get a significant percentage of the swing voters,” said William G. Mayer, a professor of political science at Northeastern University who has written extensively about swing voters. “I know Republicans who think that Trump is somehow incredibly savvy politically and knows just what he’s doing. I strongly disagree. I think he’s needlessly alienating a whole lot of people who might otherwise be inclined to vote for him.”

The Times poll found that undecided voters do not trust Mr. Trump to provide accurate information about the pandemic, and think he uses the presidential podium to promote falsehoods.

And in a finding that pollsters tend to watch closely (sometimes wisely, but sometimes not) for an indication of where a still far-off election might go, they believe the country is heading in the wrong direction.