This article examines the alteration of the role, prerogatives, and power of the special assistant to the president for national security affairs, a position more commonly known as the national security adviser. Presidents Truman and Eisenhower conceived of and shaped the National Security Council(NSC) and its staff to be administrative in their responsibilities and character. Under President Kennedy, McGeorge Bundy utterly changed this, concentrating power and decision‐making authority in the hands of the special assistant and his NSC staff at the White House. From 1961, the special assistant and NSC staff ceased to be administrators and became policy formulators actively engaged in the policy‐making process. This transformation occurred largely at the expense of the State Department and had profound consequences for American foreign policy, particularly toward the conflict in Vietnam.