Swearing-In ceremony for Robert Porter Jackson as new U.S. Ambassador to Ghana Ambassador Jackson has a long history of service in Africa. He has served as the U.S. Department of State’s Principal Deputy Assistant Secretary for African Affairs since October 2013. From 2010 to 2013 he was the U.S. Ambassador to the Republic of Cameroon. left person: Robert Porter Jackson right person: Linda Thomas-Greenfield "(Assistant Secretary of State for African Affairs of the U.S. government)"