”I try to work out three times a week in the fitness center, and if there’s two or three members there, that’s a lot,” said Mr. Brooke, a 74-year-old Democrat who has been a member since 1992, long before Mr. Trump bought the resort. “Very often I’m the only person in the members’ changing room. Golf has also been very quiet. I’ve noticed far fewer conventions.”

The club has recently had disputes with some members who have been told they will have to wait many years, if not decades, to get refunds on golf club membership deposits, The Miami Herald reported this month. Five members have asked Mr. Brooke to find them a lawyer willing to sue the resort to get their deposits back, he said, though he intends to keep his membership.

The property has struggled since Mr. Trump bought it out of bankruptcy in 2012 for a reported $150 million. The resort lost $2.4 million in 2014. In 2016, shortly after $250 million in renovations were completed, the PGA Tour announced that while Mr. Trump was running for president it was moving the resort’s annual golf tournament — which had brought international attention to the site for more than five decades — to Mexico City.

The Trump Organization has disputed suggestions that the golf club has struggled, beyond acknowledging a local drop in demand after a Zika virus outbreak in 2016 and Hurricane Irma in 2017.

“Doral is doing great and had its best year in 2018,” the Trump Organization said in a statement in May explaining the performance of its real estate holdings last year.

The resort has benefited, in at least some ways, from Mr. Trump’s time in office. Records show that the golf club has collected at least $1.4 million in payments from Republican political groups, making it the third-most frequent venue for political operatives. The two others are the president’s Mar-a-Lago estate in Palm Beach and the Trump International Hotel in Washington, according to an analysis by Citizens for Responsibility and Ethics in Washington.

Since taking office, the president has repeatedly allowed the conduct of his official duties to be entangled with the facilities he owns. He hosted President Xi Jinping of China at Mar-a-Lago for a summit in 2017. He has made presidential stops to his golf club in Ireland. And he frequently conducts business or attends events at other locations he owns, including the Trump hotel in Washington and his club in Bedminster, N.J.