In late June, federal agents working on a complex investigation were secretly positioned at the Buffalo Niagara International Airport, tracking a potentially key witness — a top international swimming official involved in the Olympics.

The official, Brent Nowicki, was returning to Europe after attending the U.S. Olympic swimming trials in Indianapolis.

Before he could board, the agents presented a startled Mr. Nowicki with a grand jury subpoena, demanding that he testify in a federal investigation into whether global sports authorities covered up positive tests by elite Chinese swimmers for a banned performance-enhancing drug.

Even before the encounter, the Chinese positive tests had already become an Olympics controversy. But approaching Mr. Nowicki, only weeks before the start of the Summer Games in Paris, escalated the situation into a broader confrontation over the power to police global sports, with consequences possibly extending to who is allowed to host an Olympic Games.

Soon after the subpoena was delivered, officials with the International Olympic Committee and the World Anti-Doping Agency began a pressure campaign to shut down the federal investigation. Olympic officials threatened to hold up two things considered shoo-ins — the awarding of the 2034 Winter Games to Salt Lake City and the elevation of the top U.S. Olympics official, Gene Sykes, to the powerful International Olympic Committee.

This all burst into view in late July, days before the opening ceremony in Paris: In an extraordinary public spectacle, Olympic officials staged a dramatic power play, pressing Mr. Sykes and other American officials to help end the federal inquiries as a condition for receiving the bid.