A bipartisan group of U.S. senators sent a letter Wednesday to the leader of the World Anti-Doping Agency asking for answers about the case in which 23 Chinese swimmers were cleared to compete at the Tokyo Olympics despite positive tests for a banned drug. “It is not just this one incident that causes concern for many athletes, anti-doping agencies, and fans across the world, but it is the fact that WADA has long shown questionable ethical behavior,” said the letter sent from Sens.