In 1966 Warnke became general counsel to the Department of Defense. He was appointed assistant secretary of defense for international security affairs the following year. He firmly opposed American involvement in Vietnam. His views had a substantial impact on Secretary of Defense Robert McNamara and his 1968 successor, Clark Clifford. Originally a strong supporter of U.S. intervention, Clifford instigated new studies of the war, whose findings rapidly led him to advocate U.S. withdrawal.
When President Lyndon B. Johnson left office in 1969, Warnke joined Clifford's law practice but continued to advise Democratic presidential hopeful Edmund S. Muskie and the 1972 nominee, George S. McGovern. A strong advocate of major cuts in defense spending and freezes on the development and production of new weapons system, Warnke argued that reining in the arms race demanded that both superpowers exercise restraint. Claiming that asymmetrical nuclear balances were largely irrelevant to security, in 1975 he publicly urged that the United States should take the lead in demonstrating unilateral nuclear restraint. During the presidencies of Republicans Richard M. Nixon and Gerald R. Ford, Warnke was a prominent supporter of the protracted Strategic Arms Limitation Talks (SALT) and the SALT I and Anti-Ballistic Missile (ABM) Treaties negotiated in 1972.
Warnke's conciliatory views were anathema to the more hawkish foreign policy officials, notably Democratic Senator Henry M. Jackson and Warnke's former colleague Paul H. Nitze, clustered in the Committee on the Present Danger, founded in 1976 to press for major increases in American defense expenditures, the development of additional weapons systems, and more cautious arms control policies. In 1977 incoming Democratic President Jimmy Carter appointed Warnke director of the Arms Control and Disarmament Agency (ACDA) and chief SALT negotiator. Forty senators voted against his SALT appointment, and in office he remained a persistently controversial figure. In November 1978, with the SALT II Treaty about to seek Senate ratification, he decided to return to his law practice.
Warnke remained a special consultant on arms control to the secretary of state until 1981. Throughout the 1980s and 1990s he continued to speak and write extensively on arms control and other international issues. In 1995 he joined President William Jefferson Clinton's Advisory Board on Arms Control and Non-Proliferation Policy. Warnke died in Washington, D.C., on 31 October 2001.
Glynn, Patrick. Closing Pandora's Box: Arms Races, Arms Control and the History of the Cold War. New York: Basic Books, 1992.; Herken, Gregg. Counsels of War. New York: Knopf, 1985.; Nolan, Janne E. Guardians of the Arsenal: The Politics of Nuclear Strategy. New York: Basic Books, 1989.; Talbott, Strobe. The Master of the Game: Paul Nitze and the Nuclear Peace. New York: Knopf, 1988.