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Rh can operate only externally, in the context of lands under the purview of another sovereign (like Indian tribal lands) or in the context of a government-to-government relationship (such as matters of diplomacy or peace). See Curtiss-Wright, 299 U. S., at 315, 319. But regulating child custody proceedings of citizens within a State is the paradigmatic domestic situation; the Federal Government surely could not apply its foreign-affairs powers to the domestic family-law or criminal matters of any other citizens merely because they happened to have citizenship or ancestral connections with another nation. Apart from the single provision that allows tribal governments jurisdiction over proceedings for Indians on tribal lands, see §1911(a), ICWA is completely untethered from any external aspect of our Nation that could somehow implicate these powers.

That should be the end of the analysis. Again, as the majority notes, our Federal Government has only the powers that the Constitution enumerates. See ; McCulloch, 4 Wheat., at 405. Not one of those enumerated powers justifies ICWA. Therefore, it has no basis whatsoever in our constitutional system.

Even taking our “plenary power” precedents as given (as