Unscrupulous and devious in many ways, President Nixon was the consummate realist in foreign policy, especially when guided and prodded by his national security affairs adviser, the German émigré and former Harvard professor Henry A. Kissinger. Upon learning that the Soviets were rapidly approaching nuclear parity with the United States, the new president sensibly abandoned the quixotic search for American superiority in nuclear weapons systems and accepted the concept of parity or "sufficiency." He simultaneously made the decision to expand ABM defenses in the name of damage limitation, citing not only the danger from the Soviet Union but also from the People's Republic of China, which recently had joined the special weapons club by testing and deploying a nuclear weapon. Unlike Sentinel, however, the new Nixon Safeguard system was designed exclusively to protect Minuteman ICBM silos. The administration made public its decision that, in light of the Soviet Union's burgeoning offensive nuclear capability, limiting damage to civilian targets no longer was possible. The United States could only hope to preserve a retaliatory capability, the existence of which would deter an opponent from striking first. To further underscore his tough-mindedness and enhance the American retaliatory arsenal, Nixon installed more MIRVs on U.S. ICBMs.
Considering himself to be in a position of diplomatic strength, President Nixon entered into the Strategic Arms Limitation Talks (SALT) negotiations with the Soviet Union in November 1969. The Soviets, for their part, were now willing to negotiate because they were drawing abreast of the United States in numbers of ICBMs, if not in MIRVed warheads. A rough de facto nuclear parity had been achieved, and each side sought to freeze it in order to avoid the astronomical expense of building elaborate ABM systems, which existing technology could not make fully effective. The cost of the Vietnam War was driving American fiscal prudence; the chronic inefficiency of the Soviet economy was inspiring Moscow's circumspection. The two sides, however, were unable to reach any agreement and the SALT I discussions dragged on until the spring of 1972.
Fruition came at a summit in Moscow on 26 May 1972, when the Soviet Union and the United States agreed by treaty to curtail deployment of ABMs. Delegates of the two superpowers also initialed a five-year interim agreement freezing offensive strategic nuclear weapons systems at their existing levels. In essence, the United States conceded to the Soviet Union an advantage in large missiles with horrifically destructive warheads, and the Soviet Union yielded to the United States the countervailing advantage in MIRVs. "What are 3,000 MIRVs among friends?" Henry Kissinger joked, but he later regretted that he had not pondered "the implications of a MIRVed world more thoughtfully."
The ABM Treaty likewise failed to prohibit further development of new delivery systems, such as the supersonic intercontinental B-1 bomber to replace the B-52, longer-range Trident SLBMs to replace the Polaris-Poseidon system, and nuclear-tipped cruise missiles. Maintenance of nuclear parity at the 1972 level, therefore, gave the United States the chance to capitalize on its technological supremacy to make an end run on the Soviets. With characteristic insight and cynicism, Kissinger quipped, "The way to use this freeze is for us to catch up." The Senate showed its appreciation for the advantages of the ABM Treaty by approving it with an overwhelming vote: 88 to 2. A joint congressional resolution endorsed the five-year moratorium on development of new offensive strategic nuclear weapons.
Nixon's acceptance of atomic equality did not deter him from relying on nuclear weapons in his conduct of foreign and military policy. For example, during the 1973 Yom Kippur War in the Middle East, he authorized a full alert of American strategic forces to forestall intervention by Soviet airborne troops. Similarly, as he progressively reduced the size of the U.S. Army, he permitted his advisers to revive plans for using tactical, or battlefield, nuclear weapons. In January 1971, when speaking about the American defense posture from 1972 through 1976, Secretary of Defense Melvin B. Laird said: "For those levels in the deterrent spectrum below general nuclear war, the forces to deter Soviet and Chinese adventures clearly must have an adequate war-fighting capability, both in limited nuclear and conventional options."
Hoping to capitalize on the success of the ABM Treaty, Nixon ordered new negotiations with the Soviet Union. SALT II opened with promise in November 1972 but soon foundered for several reasons: the scandal of the Watergate burglary and the forced resignation of Nixon in August 1974, Soviet-American disagreements over technical issues, and the objections of militants like Senator Henry Jackson who cried for the restoration of nuclear superiority.