The allegations against Mr. Trump have followed a White House campaign to end the “rape culture” on college campuses and address what many students and liberals view as a permissive attitude toward sexual assault. Some college students said they were stunned that Mr. Trump still enjoyed relatively strong support in spite of his comments about women and the allegations against him, but added that many voters had already made up their minds and were unlikely to swing toward Mrs. Clinton solely on the issue of sexual misconduct.

“The idea that a candidate with a major-party backing has allegations of this nature on his record is vile,” said Alex Abbott, 20, a senior at Hampden-Sydney College, an all-male campus in Virginia. Still, he added, the responses to Mr. Trump’s behavior that Mr. Abbott had heard from men “are either ‘I would never do anything like that,’ or ‘Every guy does that, and it’s not out of the ordinary.’”

While surveys show voters are chiefly concerned about the economy and terrorism, the drumbeat of negative attention on Mr. Trump’s sexual behavior is hurting him with female voters and independents, according to Republican pollsters. But support for Mrs. Clinton has not jumped noticeably, a sign that many Republicans still do not see Mr. Trump as morally unacceptable — at least compared with the Clintons.

“It’s what I have termed negative partisanship,” Alan Abramowitz, a political science professor at Emory University in Atlanta, wrote in an email. “We vote against the other party/candidate more than for our own party/candidate, and that is especially true this year for Republicans.”

The ill will for Mr. Trump is just as strong among Democrats like Jon Robin Baitz, an acclaimed Broadway playwright whose latest work, “Vicuña,” explores a tailor’s relationship with a blustering Trump-like candidate, and will run this fall at the Kirk Douglas Theater in Los Angeles.

“My heart is broken,” Mr. Baitz said. “There is, to me, a kind of fundamental American decency, and it’s just been lost in the prurient shallowness of the discourse.”