Answer: War Powers Act
Step-by-step explanation:
Even though the United States was heavily involved in the Vietnam War, they never actually declared war. This along with President Nixon bombing Cambodia without Congressional approval alarmed Congress as they felt that their Constitutional power to declare war was being eroded.
In response, they passed the War Powers Act that limited the power of the President to commit the American military to actions in other countries over a long period of time. President Nixon vetoes this but with a two-thirds majority in Congress (both houses) voting for the bill, his veto was overridden.