Within 10 minutes, 48 people were lined up behind her.

A carnival atmosphere filled the boardwalk nearby, as supporters of Mr. Trump mingled near a blocklong corridor of T-shirt and button vendors. Some heckled a group of protesters who were cordoned off in a parking lot below, resulting in a volley of competing chants.

“Four more years,” Mr. Trump’s supporters shouted.

“Dump that Trump,” the protesters answered.

Marianne Bryant, a lawyer from Voorhees, N.J., said she had taken a day off from work to be part of the protest, her first.

“I feel like this nation is definitely headed on the wrong track,” Ms. Bryant, 68, said. “I haven’t been this scared since the Vietnam War. I don’t think we can take four more years of him.”

All eyes were fixed on a Jumbotron in the convention center parking lot as Mr. Trump took the stage just before 7:30 p.m. The crowd outside erupted in applause and chants of “U.S.A., U.S.A.” Mounds of debris, chairs, blankets and food filled the parking lot as a steady flow of people began to drift away.

Mike Whilden, of Millville, N.J., stood watching the Jumbotron until the end.

“He doesn’t mince words,” Mr. Whilden, 63, said. “He’s a straight shooter.”

Mr. Trump’s decision to stage one of his raucous rallies in Wildwood, motivated by a desire to support a local congressman who recently switched parties, upended the usual rhythms of this beach community about 160 miles south of New York City.