Whether a State May Exercise Juridiction That the US is Entitled to Exercise Under International Law is a Question of US Law Not International Law:
In Skiriotes v. Florida, 313 U.S. 69, 85 L. Ed. 1193, 61 S. Ct. 924 (1941), the United States Supreme Court rejected the defendant's argument that the State was preempted from exercising extraterritorial jurisdiction because it would encroach upon the exclusive treaty-making power of the United States. 313 U.S. at 71-72. Instead, the Court reasoned that because the United States would have been able to exercise jurisdiction, the question of whether the State could also exercise jurisdiction was one of federal rather than international law. See id. at 75-77.
In Skiriotes, the Court stated that a key factor in its holding was that Florida's criminal jurisdiction was based upon the prosecution for an alleged crime committed by a Florida resident:
Even if it were assumed that the locus of the offense was outside the territorial waters of Florida, it would not follow that the State could not prohibit its own citizens from the use of the described divers' equipment at that place.
No question as to the authority of the United States over these waters, or over the sponge fishery, is here involved.
No right of a citizen of any other State is here asserted.
The question is solely between appellant and his own State.
The case thus differs from that of Manchester v. Massachusetts, supra, [139 U.S. 240, 35 L. Ed. 159, 11 S. Ct. 559] for there the regulation by Massachusetts of the menhaden fisheries in Buzzards Bay was sought to be enforced as against the citizens of Rhode Island and it was in that relation that the question whether Buzzards Bay could be included within the territorial limits of Massachusetts was presented and was decided favor of that Commonwealth.
The question as to the extent of the authority of a State over its own citizens on the high seas was not involved.
International law is not concerned with the question of whether this defendant is prosecuted by a state or the federal government.
As a comment to the Restatement (Third) of Foreign Relations (1986) [hereinafter Restatement], explains:
Since international and other foreign relations law are the law of the United States, under the Supremacy Clause of the Constitution an exercise of jurisdiction by a State that contravenes the limitations of §§ 402-403 is invalid. . . .
International law normally is not concerned with how authority to exercise jurisdiction is allocated within a state's domestic constitutional order.
Whether a State may exercise jurisdiction that the United States is entitled to exercise under international law is, therefore, generally a question only of United States law.
Subject to constitutional limitations, a State may exercise jurisdiction on the basis of territoriality, including effects within the territory, and, in some respects at least, on the basis of citizenship, residence, or domicile in the State. Id. at § 402 cmt. K.