Final answer:
The requirement for the President to report to Congress about troop deployments within 48 hours and seek approval within 60 days is established by the War Powers Act of 1973, aimed at curbing executive power post-Vietnam.
Step-by-step explanation:
The requirement that the President must report to Congress within 48 hours of sending troops into hostilities and then obtain approval from Congress within 60 days is established by the War Powers Act. This Act was passed in 1973 in the wake of the Vietnam War as a means to limit the President's ability to commit U.S. troops without Congressional authorization. While the Act was intended to strengthen the role of Congress in matters of war, it also clarified that the President could act on their own for sixty days without Congressional approval which, in practice, has allowed Presidents to commit troops with minimal immediate oversight.