War Power Act is a federal law created to control the power of the president to engage in armed conflicts with other nations without the approval of the U.S. Congress.
Among other stipulations, it requires that the president notifies the congress 48 hours prior to sending military forces to action, and forbids them to stay longer than 60 days in missions, with and extra 30 day period for withdrawing.
It relates to the President in a way that in the 20th/21st century, it's very important to have this kind of regulations, to prevent wars, and rushed decisions of going to battle. Nowadays, weapons are deadlier than ever, and an atomic war is a real possibility, and efforts like these help prevent it.