Relationship of international law and municipal law — Conduct of foreign relations — United States — Foreign affairs power shared between Congress and the Executive — Division of power — Anti-Terrorism Act 1987 — Effect on Palestine Liberation Organization activities within the United States — Determination by Legislature that United States interests would be served by curtailing such activities entitled to respect from courts — Whether Act contrary to First Amendment to United States Constitution — Application of national law to foreign States and entities — Whether official of foreign State or entity may assert constitutional rights to prevent the adoption of foreign affairs measure affecting foreign State or entity — The law of the United States