The transformation of American political system, especially the changes in the relationship between the executive and the legislative branches, affects the formulation of American international trade policy in a major way. Under the separation of power, the creation and transformation of the role of the Office of U.S. Trade Representative (USTR) reflect the struggle between the President and the Congress over the policymaking power over international trade. The Congress constantly challenges the executivedominated “1934 pattern” and tries to establish a new international trade system to be jointly managed by the President and the Congress. The changes in the relationship between the two branches not only determine the power and role of the USTR but also affects its behavior in world trade negotiations.