Treaties and the Constitutional Separation of Powers in the United States
The Constitution wholeheartedly accepted Montesquieu’s theory of the separation of the powers of government into three departments, and the courts have maintained as a fundamental principle of constitutional law that no department shall exercise powers properly belonging to either of the others. The treaty-making power is established in Article II of the Constitution dealing with the executive, and consequently treaty-making has been ordinarily considered one power of the executive department. It is, however, stated that “the executive power shall be vested in a President of the United States of America,” whereas the treaty-making power is vested in the President acting “by and with the advice and consent of the Senate — provided two-thirds of the senators present concur.” Furthermore “treaties made … under the authority of the United States” are “the supreme law of the land.” Thus, both by composition and function the treaty-making power appears to be fully as much legislative as executive, a situation emphasized by Hamilton in the Federalist.