Both Candidates Are Widely Disliked (Again). This Time, Biden Could Benefit.

In the days immediately leading up to the 2016 election, a Monmouth survey had found an even greater share of voters — 34 percent — saying they did not like either Mrs. Clinton or Mr. Trump. In that poll, Mrs. Clinton had a slimmer edge over Mr. Trump among those voters. After the election, exit polls and other postmortem polling found that they had in fact swung hard in Mr. Trump’s favor, with many changing their minds at the last minute.

Thanks in large part to those voters, he squeaked by with an Electoral College victory, even though more people actually said they disliked him (60 percent) than said they disliked Mrs. Clinton (55 percent), according to exit polls.

The picture this year is different. Americans’ views of the president have hardened in place, and far fewer who dislike him are likely to vote for him again.

“If you’re a Trump voter, you don’t like him — you love him,” Frank Luntz, a veteran Republican pollster, said in an interview. “And nothing said by cable news or media is going to change that.”

He added, “But in the end, if you don’t like him, you’re just as passionate.”

Indeed, few voters express a mild view of Mr. Trump. In the Monmouth poll, 48 percent of the country had a “very unfavorable” view of him, while just 9 percent had a “somewhat unfavorable” opinion.

For Mr. Biden, that wasn’t the case.

“With Biden, you see a much more even split in his unfavorability rating,” Mr. Cecil said. “Among swing voters — to the extent that we have a shrinking number of swing voters — their views of Trump are much more intense than their views of Biden.”

And while Mr. Trump’s ratings have stayed relatively stable, Mr. Biden’s favorability numbers have been more fluid. Until last summer, most Americans held a positive view of the former vice president; it was only when his presidential run heated up that his favorability rating began to dip into negative territory, partly the result of attacks from his Democratic rivals.