How did President Ronald Reagan’s Strategic Defense Initiative challenge mutual assured destruction?

President Ronald Reagan’s Strategic Defense Initiative (SDI) challenged the doctrine of mutual assured destruction by attempting to shift the foundation of national security from deterrence through vulnerability to defense through technology.12

Under the doctrine of mutual assured destruction, both the United States and the Soviet Union maintained stability by ensuring that any nuclear attack would result in the total annihilation of both parties. By proposing a system capable of intercepting and neutralizing incoming intercontinental ballistic missiles, SDI threatened to undermine this "assured-destruction capability".21

Critics argued that this shift was dangerous because it broke with the established status quo, potentially incentivizing the Soviet Union to launch a preemptive strike before the system could be fully deployed. Furthermore, opponents contended that the initiative would trigger a new arms race and violate existing arms-control agreements, such as the 1972 ABM Treaty. While proponents viewed SDI as a moral effort to liberate the world from the fear of nuclear holocaust, the program fundamentally challenged the logic of a stalemate that had defined the Cold War for decades.132