JOHANNESBURG — Inspired by Nelson Mandela's struggles in South Africa, a young Barack Obama joined campus protests in the U.S. against the racist rule that kept Mandela locked away in prison for nearly three decades. Now a historic, barrier-breaking figure himself, President Obama arrived in South Africa Friday to find a country drastically transformed by Mandela's influence — and grappling with the beloved 94-year-old's mortality. It was unclear whether Mandela's deteriorating health would allow Obama to make a hospital visit.