Mr. Trump “is no stranger to untruthful journalism and venomous attacks from the liberal media; however, our little girls were not,” Mr. Popick wrote in the email, which was provided to The New York Times.

Mr. Popick started the group two and a half years ago. He said his daughter and the other girls were natural performers who could not get enough of being on stage. They’ve had gigs at local sporting events and performed outside the Rock and Roll Hall of Fame in Cleveland last week during the Republican National Convention.

Mr. Popick said he had even reached out to Hillary Clinton about a performance before she declared her intent to run for president.

“We were saying to her, she’s an accomplished woman and I’m sure the girls would love to perform with her,” he said. He did not hear back.

After Mr. Trump announced his candidacy last summer, Mr. Popick contacted various members of the campaign staff. He said he asked for $2,500 for the Jan. 13 appearance in Pensacola, but a staff member instead offered a table to sell the group’s merchandise outside the event. But when they arrived, there was no table, Mr. Popick said, calling it a breach of contract.

Even so, the campaign asked the group to perform again, he said.

About two weeks later, a campaign staff member called him and asked if the group could perform at an event in Des Moines the next day. Mr. Popick said he agreed it would be “huge exposure,” so he quickly bought nonstop flight tickets to Chicago for himself; his wife, Debbie; his daughter and two other girls.

But when they landed, planning to make the roughly five-hour drive to Des Moines, Mr. Popick was told that there would be no performance at the event. The group went instead as guests of the campaign, the girls wearing their costumes. Mr. Popick said he was not reimbursed for their travel costs.