for their acts of a public charac- ter."); Letter from Arnold Kanter, Acting Secretary of State, to Presi- dent George H. W. Bush (Sept. 12, 1992) in Digest of United States Practice in International Law 1016-1017 (S. Cummins & D. Stewart eds. 2005) (explaining that the Headquarters Agreement of the Organi- zation of Amer