Final answer:
The US Congress refused to ratify the SALT II treaty due to concerns about national security.
Step-by-step explanation:
The US Congress responded to the signing of the SALT II (Strategic Arms Limitation Talks) treaty by refusing to ratify the treaty. Despite the efforts of President Carter to gain support for the treaty, Congress did not approve it due to concerns that the treaty would endanger US national security by trusting the Soviets to adhere to its provisions.