Reuben Brigety spent three years of his life trying to help African nations develop their own governments. Now, as the retired U.S. ambassador looks at the United States, he’s concerned that the country is at risk of losing its values under President Donald Trump. “This great experiment we have is not guaranteed to stay forever,” Brigety warned a group of about 25 people during a Wednesday lecture at the University Club in Oakland. To keep the experiment in democracy and freedom alive, Brigety suggested an agenda of political activism, community engagement and faith in other Americans. Brigety, who lives in Washington, D.C., represented the United States at the African Union from 2013 to 2015, and has held other positions within the Department of State.