On a Monday in March, in the heart of China’s capital, more than 2,000 delegates of a rubber-stamp advisory body to the authoritarian government of President Xi Jinping gathered for their annual meeting.

One mission of the men and women in attendance was to spread the global influence of China’s Communist Party. Of the throngs of party officials, generals and business executives who watched as Mr. Xi took the stage, just 20 people had been invited to represent the country’s vast diaspora, including a single person from the United States: a 69-year-old man from Brooklyn named John Chan.

Mr. Chan’s participation reflected a remarkable proximity to the highest levels of power in China, experts said, and marked him as a person on whom the country’s leaders might call for favors. But it was remarkable, too, because of his position at home: He has operated as a power broker in America’s largest city, with immense sway over an important subset of New York politics.

For years, Mr. Chan has exerted influence over the city’s ethnic Chinese communities — reaching into back rooms and political clubhouses from Sunset Park in Brooklyn to Manhattan’s Chinatown to Flushing in Queens — to help sway elections, all without drawing much attention.

But lately, federal investigations into foreign influence efforts have swirled around city and state government in New York. Mayor Eric Adams has been charged with conspiring to accept illegal foreign campaign contributions from Turkey. He has pleaded not guilty. One of his top aides, an Asian affairs director with ties to China, had her homes searched in an investigation by Brooklyn federal prosecutors who have separately brought cases against people they suspect of being Chinese agents.

The same prosecutors recently accused an aide to Gov. Kathy Hochul of serving the Chinese government by blocking Taiwanese officials from the governor’s office.