Most stark may be Mr. Biden’s towering advantage among white women with college degrees, who support him over Mr. Trump by 39 percentage points. In 2016, exit polls found that group preferred Mrs. Clinton to Mr. Trump by just 7 percentage points. The poll also found that Mr. Biden has narrowed Mr. Trump’s advantage with less-educated white voters.

The exodus of white voters from the G.O.P. has been especially pronounced among younger voters, an ominous trend for a party that was already heavily reliant on older Americans.

Fifty-two percent of whites under 45 said they supported Mr. Biden while only 30 percent said they supported Mr. Trump. And their opposition is intense: More than twice as many younger whites viewed the president very unfavorably than very favorably…

What’s striking, though, is that even among white seniors, one of Mr. Trump’s strongest constituencies, he has damaged himself with his conduct. About two-fifths of whites over 65 said they disapproved of Mr. Trump’s handling of both the coronavirus and race relations.