Final answer:
The U.S. responded to the Soviet invasion of Afghanistan by boycotting the 1980 Olympics, imposing economic sanctions including halting grain shipments, withdrawing SALT II from Senate consideration, and supporting the anti-Soviet mujahideen.
Step-by-step explanation:
The United States responded to the Soviet invasion of Afghanistan in several significant ways. President Jimmy Carter imposed economic sanctions and called for an international boycott of the 1980 Olympic Games in Moscow, which marked a clear political statement against Soviet actions. Additionally, the U.S. government removed the Strategic Arms Limitation Talks II (SALT II) from consideration in the Senate, signaling a tough stance on arms control with the USSR.
To directly counter the Soviet military presence in Afghanistan, the U.S. stopped shipments of grain to the Soviet Union and provided covert support to the mujahideen, the Islamic insurgents fighting against the Soviet forces, by supplying money, arms, and surface-to-air missiles. This support was instrumental in the eventual withdrawal of Soviet troops from Afghanistan.
Thus, by boycotting the 1980 Olympics, halting grain shipments, removing SALT II from consideration, and supporting the mujahideen, the U.S. took multifaceted actions to respond to the Afghanistan crisis and oppose the Soviet invasion.