She compared him to Hitler, likened his campaign to a “racist” version of “Fun with Dick and Jane” and even said he evoked the murderous child star in “The Bad Seed.”

“I just think he’s” an idiot, Cher said of Donald J. Trump, adding a decidedly unprintable modifier.

The crowd on Sunday in Provincetown, Mass., one of the country’s gay capitals, roared its approval at Cher’s succinct and salty assessment. But the famed singer and actress was not just riffing between songs at a concert: She was introducing Hillary Clinton at a fund-raiser for her presidential campaign.

Cher did more than just blister Mr. Trump. She also offered a blunt appraisal of Mrs. Clinton’s strengths and weaknesses. “This chick is just tougher than Chinese algebra,” Cher said of the Democratic nominee.