The Curse of Apollo has lasted for 136 years, but Justify has a strong chance to make history by winning the Run for the Roses after not racing as a 2-year-old LOUISVILLE, Ky.—Bob Baffert is a four-time Kentucky Derby-winning trainer with a stable full of champion thoroughbreds, most recently sweeping the Triple Crown with American Pharoah in 2015. He often works with the sport’s best horses, so it wasn’t particularly noteworthy when a young colt named Justify entered his barn late last year. “I just can’t remember offhand,” Baffert said last month about his earliest memories of Saturday’s Kentucky Derby...