Basically, the voters.
[T]he people seems to have been a term of art employed in select parts of the Constitution. The Preamble declares that the Constitution is ordained and established by the People of the United States. The Second Amendment protects the right of the people to keep and bear Arms, and the Ninth and Tenth Amendments provide that certain rights and powers are retained by and reserved to the people. See also U.S. CONST., amdt. 1; Art. I, § 2, cl. 1."
"While this textual exegesis is by no means conclusive, it suggests that the people protected by the Fourth Amendment, and by the First and Second Amendments, and to whom rights and powers are reserved in the Ninth and Tenth Amendments, refers to a class of persons who are part of a national community or who have otherwise developed sufficient connection with this country to be considered part of that community."
-- United States v. Verdugo- Urquidez, 494 U.S. 259 (1990)
Not every individual. Not every person. Not even every citizen.