Under the Tenth Amendment, there are three possibilities: (i) If a power is delegated to the United States by the Constitution, it is not reserved to the States * * * or to the people”. (ii) If a power is “reserved to the States * * * or to the people”, it is not “delegated to the United States”. And (iii) if a power is “prohibited by [the Constitution] to the States”, it is either “delegated to the United States” or “reserved * * * to the people”.