What was President Eisenhower's stated policy for deterring a Soviet nuclear strike?
Massive retaliation, now known as Mutually Assured Destruction (MAD for short).
Immediately after the end of World War II, the United States was the only nation that had a nuclear weapon. However, in 1949 the Soviet Union detonated its own nuclear device.
The two countries were antagonists with different economic systems, government systems, and views on how the world should be run. As a consequence, the United States was constantly worried that the Soviet Union would attack America's allies in Western Europe or the United States itself.
Since there was no way to prevent or intercept nuclear weapons at that time, the doctrine adopted by Eisenhower and his successors has been that if the Soviet Union attacked either the US or its allies, the United States would be able to launch enough nuclear weapons to guarantee that the Soviet Union would be destroyed as well. It was a case of, "I may die, but I'll be sure to take you with me."
Except for a few brief incidents where it was thought that the end had come, that policy has prevented the world from being destroyed by nuclear war.