Ndileka Mandela, the eldest granddaughter of the late former South African president, Nelson Mandela, was meant to have politics woven into her life. As a child, it meant visiting her grandfather in prison as he served time for fighting apartheid. But last month, Ndileka, 52, opened Facebook on her computer and posted a picture of herself voting with her grandfather in 2011. Then she swallowed hard and began to type: “I will no longer vote for the ANC.” Since Nelson Mandela’s death in 2013, the ANC has been plagued by scandals, internal divisions and electoral losses. But no member of the Mandela family disowned the party. Twenty-three years after the birth of democracy here, a surging number of South Africans are asking themselves whether the movement that defeated apartheid still deserves to lead the country. Much of the criticism is directed at President Jacob Zuma, whose two terms have been marked by corruption allegations.