Diplomatic relations — Treaties — Vienna Convention on Diplomatic Relations, 1961, Article 22 — Duty of States Parties to protect foreign embassies — Duty to protect any disturbance of peace of mission or impairment of its dignity — United States statute prohibiting display of placards bringing a foreign government into disrepute within 500 feet of the embassy (“display clause”) and persons congregating within 500 feet of the embassy (“congregation clause”)

Relationship of international law and municipal law — United States Federal Constitution — Guarantees of free speech and equal protection in First and Fourteenth Amendments to Constitution — Whether United States statute violating First Amendment — Constitutionality of display clause — Constitutionality of congregation clause — Whether statute serving compelling governmental interest — Role of court in assessment — United States’ obligations under international law — Article 22 of Vienna Convention on Diplomatic Relations, 1961 — Whether display and congregation restrictions permissible — Whether less restrictive alternative available — Whether United States statute achieving permissible accommodation between competing claims of fulfilment of international obligations and protection of freedom of expression enshrined in Federal Constitution — The law of the United States of America