The president plays a key role in shaping foreign policy as the chief diplomat and commander-in-chief. They appoint ambassadors, negotiate treaties, and engage with foreign leaders, guiding national interests on the global stage. The president can also establish directives, propose military action, and utilize international agreements to strengthen alliances. However, they must share this power with Congress, which has authority over appropriations and ratifying treaties, leading to a complex interplay of responsibilities in foreign affairs.