Having already joined the banned PSOE left-wing party in 1964, he became one of its leaders when it became legal in 1977. He became a Cabinet Minister, serving first as Minister for Culture and party spokesman, then Minister for Education, then Minister for Foreign Affairs, before being made NATO boss in December 1995, just as the Dayton agreement saw the IFOR NATO peacekeeping mission enter the former Yugoslavia. He was also involved in the Kosovo bombings, and the negotiations that led to an eventual peace.