The Founders clearly expected that the customary law of nations was binding, was supreme law, created (among others) private rights and duties, and would be applicable in United States federal courts. For example, at the time of the formation of the Constitution John Jay had written: "Under the national government… the laws of nations, will always be expounded in one sense… [and there is] wisdom… in committing such questions to the jurisdiction and judgment of courts appointed by and responsible only to one national government...” In 1792, the supremacy of the customary law of nations within the United States was affirmed in Ross v. Rittenhouse; and Attorney General Randolph declared: "The law of nations, although not specially adopted… is essentially a part of the law of the land."
Jordan J. Paust,
Customary International Law and Human Rights Treaties are Law of the United States,
Mich. J. Int'l L.
Available at: https://repository.law.umich.edu/mjil/vol20/iss2/19