ok, totally hypothetical.
Athlete A is from the United States, Athlete B is from China. Athlete A wins an event the United States has not won in a long time and appears to be the best. Athlete B finishes 4th.
Chinese leadership, desperate for an edge in the games, gives Athlete A a little local Orange Duck in the village. Athlete A tests positive in a subsequent test for trace amounts of an anabolic steroid, the IOC states however that the local food was at blame, but not the Athlete, so Athlete A is not given a doping suspension BUT does lose their medal. Athlete B goes on to win Bronze.
Hypothetically, athlete's A country of origin doesn't even matter, as long as it produces another medal for the glorious chinese nation. Anyone want to go to Beijing?