In this apprehension, the country's founding fathers seem to have given overlapping powers to Legislature and Executive, and this led Edwin Corwin to say that both branches are expected "to struggle for the privilege of directing American Foreign Policy."
This has naturally resulted in Executive and Legislature sharing the foreign policy decisions. It has also resulted in a kind of competition and jealous guarding of their spaces, which has led to unpleasant bickering many times. Constitution has laid down these principles as effective check against each other's power, and the hope of a highly gratifying foreign policy that would be helpful not only to America, but also to the rest of the world, as America is a huge and powerful nation. They had not foreseen that America would become the only super power, but they had definitely foreseen that it would be an influential power in the world, that would have a definite say in world matters. These thinkers want that clout to be a very positive one. To a very large extent, they have attained their wish, though it leads to one-upmanship very often, especially when the incumbent in White House is not a visionary.
America had gained her independence much before any other colonies and her only rival in those years was Britain in world affairs. Slowly when British power diminished after two world wars, America more or less conducted her foreign affairs on her own terms and this made the American President an invincible and all-powerful personality on the world stage. But at home, there had always been a slight, sometimes more pronounced tug of war between the Executive and Legislature, which worked as an effective check during times of stress, and an irritant, sometimes even a definite threat during other.
Treaties in US are entirely executive agreements. American presidents have made many international agreements through Congressional-Executive Agreements and only the President has the power to do so. These have to be ratified by only majority in both the Houses. Some constitutional scholars have said that these CEAs are unconstitutional, but Supreme Court has upheld their validity. Once these agreements are reached they are binding while these procedural acceptances go on.
Foreign policy is the politics of shared power between executive and legislature and these two have to maintain the balance.
The extent to which the executive power touches the foreign policy had always been a matter of controversy. Today there are many pragmatic and constitutional arguments trying to fix the boundaries of executive power on war, national security and treaty interpretation.
"Finally, the President has broad residual power over foreign affairs, but that power does not extend to matters not part of the traditional executive power. Accordingly, the President cannot claim lawmaking or appropriations power in foreign affairs" http://papers.ssrn.com/sol3/papers.cfmabstract_id=285988
American foreign policy still runs with an institutional approach where the powerful executive sometimes takes the centre stage, or a less powerful one allows the Legislature to take an upper hand. This usually results in two types of Presidents, one type, more visible, like Roosevelts and