Two months before the Olympics are scheduled to begin in Paris, the global agency tasked with policing doping in sports is facing a growing crisis as it fends off allegations it helped cover up the positive tests of elite Chinese swimmers who went on to compete — and win medals — at the last Summer Games.

The allegations are particularly vexing for the World Anti-Doping Agency, which has long billed itself as the gold standard in the worldwide movement for clean sports, because they raise the specter that the agency — and by extension the entire system set up to try to keep the Olympics clean — cannot be trusted.

Athletes are openly questioning whether WADA can be relied upon to do its core job of ensuring there will be a level playing field in Paris, where some of the same Chinese swimmers are favorites to win more medals.