By the 14th Amendment.
"The next observation is more important in view of the arguments of counsel in the present case. It is, that the distinction between citizenship of the United States and citizenship of a state is clearly recognized and established. . . .
It is quite clear, then, that there is a citizenship of the United States, and a citizenship of a state, which are distinct from each other, and which depend upon different characteristics or circumstances in the individual.
We think this distinction and its explicit recognition in this Amendment of great weight in this argument, because the next paragraph of this same section, which is the one mainly relied on by the plaintiffs in error, speaks only of privileges and immunities of citizens of the United States, and does not speak of those of citizens of the several states. The argument, however, in favor of the plaintiffs, rests wholly on the assumption that the citizenship is the same and the privileges and immunities guaranteed by the clause are the same.”
—Slaughterhouse Cases: 83 U.S. 36, 73-74 (1873)
Put down the crack pipe