The Strategic Defense Initiative (SDI) debate has revisited many arguments from an earlier period in the evolution of U.S. strategic doctrine. The new debate finds some SDI advocates repeating many of the same arguments against mutual assured destruction (MAD) made during the Nixon years by advocates of limited nuclear war and flexible response. Nixon administration spokesmen also argued that the U.S. president needed options in addition to retaliation against Soviet cities, especially if Soviet reserve forces could retaliate against previously spared U.S. cities.