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By now, Jacob Zuma’s South Africa should be careening toward the ranks of failed African states. Eight months ago, after an election anointed him president of the continent’s proudest democracy, editorialists everywhere drew thinly veiled comparisons to Zimbabwean dictator Robert Mugabe, who turned Africa’s shining light into a country that rivals only Somalia for sheer dysfunction. Even the most generous assessments had Zuma—once described as an “embarrassment” by Archbishop Emeritus Desmond Tutu—shackled by “suspicion” and “doubt” about his shambolic past, and fitness to lead Africa’s biggest economy. Yet under Zuma, South Africa has made pragmatic, positive strides in many areas, including health and the...