Millions of Kenyans are celebrating the long-awaited return of Barack Obama, who on Friday will visit his father's homeland for the first time as president to attend the 2015 Global Entrepreneurship Summit in Nairobi. Obama's visit will focus on economic development and counterterrorism efforts within the country against the Somali Islamist group al Shabaab, but it comes amid widespread abuse by Kenyan security forces of Muslims, refugees, and journalists. This has raised worries among rights advocates that he risks lending undue legitimacy to one of Africa's more unscrupulous regimes. Similar concerns have been voiced about a presidential trip to Ethiopia that...