Presidential candidates are a breed apart, often propelled by traits that have shaped their careers and have deep roots in personal histories. Often their greatest strength can turn at supernova speed into their greatest weakness. The exact qualities that set them apart from the field trip them up eventually over the long haul of a presidential campaign. Jeb Bush's DNA string might as well be tied around his neck. It's a twisting, double-edged lariat, this family inheritance, at once his greatest advantage and disadvantage. On the one hand, it makes him an immediate force in the crowded GOP presidential field. On the other hand, it saddles him with a problem of self-definition; people think they already know him, which means they see him as more of the same of something they already got. Twice. In this series of eBooks, The Washington Post is exploring in-depth all these key characteristics of the leading presidential contenders, the very characteristics that could help make one of them the country's next commander in chief-or forever sink their presidential ambitions.