The main responsibilities of the President of the United States include serving as the head of state and government, acting as the Commander-in-Chief of the military, and overseeing the executive branch. The President enforces laws, proposes legislation, and represents the nation in foreign relations. They also have the power to appoint federal officials, including judges and ambassadors, and can veto legislation passed by Congress. Additionally, the President plays a key role in shaping domestic and foreign policy.