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Rh the Indian tribes, and such power is superior and paramount to the authority of any State within whose limits are Indian tribes”).

To be clear, however, “plenary” does not mean “free-floating.” A power unmoored from the Constitution would lack both justification and limits. So like the rest of its legislative powers, Congress’s authority to regulate Indians must derive from the Constitution, not the atmosphere. Our precedent traces that power to multiple sources.

The Indian Commerce Clause authorizes Congress “[t]o regulate Commerce … with the Indian Tribes.” Art. I, §8, cl. 3. We have interpreted the Indian Commerce Clause to reach not only trade, but certain “Indian affairs” too. Cotton Petroleum Corp. v. New Mexico, 490 U. S. 163, 192 (1989). Notably, we have declined to treat the Indian Commerce Clause as interchangeable with the Interstate Commerce Clause. Ibid. While under the Interstate Commerce Clause, States retain “some authority” over trade, we have explained that “virtually all authority over Indian commerce and Indian tribes” lies with the Federal Government. Seminole Tribe of Fla. v. Florida, 517 U. S. 44, 62 (1996).

The Treaty Clause—which provides that the President “shall have Power, by and with the Advice and Consent of the Senate, to make Treaties”—provides a second source of power over Indian affairs. Art. II, §2, cl. 2. Until the late 19th century, relations between the Federal Government and the Indian tribes were governed largely by treaties. Lara, 541 U. S., at 201. Of course, the treaty power “does not literally authorize Congress to act legislatively,” since it is housed in Article II rather than Article I. Ibid. Nevertheless, we have asserted that “treaties made pursuant to that power can authorize Congress to deal with ‘matters’ with which otherwise ‘Congress could not deal.’ ” Ibid. And even though the United States formally ended the practice of entering into new treaties with the Indian tribes in 1871, this decision did not limit Congress’s power “to legislate on