Koster has had parallel careers in politics and journalism. He was a member of the Democratic National Committee from 1967 to 1996, served on many Democratic panels, and wrote presidential debate copy for Senator John Kerry in 2004. During the 1960s and '70s he reported from Panama for the Copely News Service and "Newsweek" magazine. He has reported more recently for the "New York Times" and has contributed prolifically to the Spanish language press in Panama. He was interviewed on National Public Radio about his book, "In the Time of the Tyrants"