During a career in the Foreign Service, he served as U.S. Ambassador to Finland and held a variety of other diplomatic and policy positions too numerous to mention. In 1995-96, while on leave from Carnegie Mellon University (where he taught from 1989-99), he was Principal Negotiator and Special Representative of the President for Nuclear Security and Dismantlement, and, in 2000-2001, deputy to General John Shalikashvili, the Special Advisor to the President and the Secretary of State for the Comprehensive Nuclear Test Ban Treaty.