Former President Donald J. Trump on Saturday spewed crude and vulgar remarks at a rally in Pennsylvania that included an off-color remark about a famous golfer’s penis size and a coarse insult about Vice President Kamala Harris.

The performance, 17 days before the election in a critical battleground state, added to the impression of the Republican nominee as increasingly unfiltered and undisciplined. It comes as some of Mr. Trump’s allies and aides worry that Mr. Trump’s temperament and crass style are alienating undecided voters.

It was unclear if the outbursts and insults were an expression of his frustration as the campaign grinds on or of his reflexive desire to entertain his crowds. At her own events on Saturday, Ms. Harris called attention to Mr. Trump’s temperament and his tendency to “go off script and ramble.”

Mr. Trump opened his speech at the airport in Latrobe, Pa., with 12 minutes of reminiscing about the golfer Arnold Palmer, who grew up in the Western Pennsylvania town and for whom the airport was named.

His monologue culminated in lewd remarks about the size of Mr. Palmer’s penis. Moments later, Mr. Trump gave the crowd an opportunity to call out a profanity. He went on to use that four-letter word to describe Ms. Harris.

“Such a horrible four years,” Mr. Trump said, referring to the Biden-Harris administration, as he surveyed the crowd of hundreds of people in front of him. “We had a horrible — think of the — everything they touch turns to —.”

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