escalation (a "nuclear spasm"), each believing that the other will back down after the first round of retaliation. Both problems are not unique to massive retaliation, but to nuclear deterrence as a whole. Policy shift In 1957, three years after his announcement of massive retaliation, Dulles compromised his doctrine. In recent years, he wrote in Foreign Affairs, there has been no alternative to massive retaliation, but now the response can be confined to limited targets. Historian of the Cold War, Marc Trachtenberg, finds that since the very announcement, Dulles was moving toward the flexible response. Nevertheless, Eisenhower until the end of his term continued to dismiss out of hand the very idea of restraint in general war. In 1959, he said: "Once we become involved in a nuclear exchange with the Soviet Union, we could not stop until we had finished off the enemy." There was no point to talking about "negotiating a settlement in the midst of the war," no alternative, therefore, to hitting "the Russians as hard as we could." President John F. Kennedy abandoned the policy of massive retaliation during the Cuban Missile Crisis in favor of flexible response. The Soviet nuclear MRBMs in Cuba had very short flight time to their US targets and could have crippled the SAC bomber bases before the aircraft could take off and launch massive retaliation against the Soviet Union. Under the Kennedy Administration, the United States adopted a more flexible policy in an attempt to avert nuclear war if the Soviets did not cooperate with American demands. If the United States' only announced military reaction to any Soviet incursion (no matter how small) was a massive nuclear strike, and the U.S. didn't follow through, then the Soviets would assume that the United States would never attack. This would have made the Soviet Union far more bold in its military ventures against U.S. allies and would probably have resulted in a full-scale nuclear war. Thomas Schelling's deterrence theory discusses this more sharply: "signalling", or the use of threats internationally to deter an enemy from an attack or to make demands. If signals weren't being properly addressed by the Soviet Union, if the threats were not intimidating or coercing them to remove the missiles from Cuba, then the Soviet Union would simply not have believed that the U.S.'s policy of massive retaliation held any water. By having other, more flexible policies to