Drug-tainted US sprinters lead Rio challenge

Justin Gatlin will spearhead a trio of drug-tainted US sprinters aiming to spoil Usain Bolt's Olympic swansong as athletics stumbles through the moral maze created by the Russia doping scandal. The 34-year-old Gatlin is the most obvious symbol of the logical confusion gripping this year's Olympics, where some athletes convicted of doping offences will be free to compete while others are banned. Gatlin, twice suspended for failing drugs tests, heads to Rio as the biggest threat to Jamaican rival