Even when he’s not running, Usain Bolt is there. His name and his world records hover over every track meet in every corner of the globe. The shadow he casts is even more pronounced at big meets like this — the U.S. nationals, where Bolt’s key challenger, Tyson Gay, pulled out with an injury and the other would-be contenders are a 29-year-old on a comeback from a doping conviction and an…