In the 1999 case of Saenz v. Roe, Justice John Paul Stevens, writing for the majority, said that the “right to travel” also has a component protected by the Privileges or Immunities Clause of the Fourteenth Amendment:^[18]

Despite fundamentally differing views concerning the coverage of the Privileges or Immunities Clause of the Fourteenth Amendment, most notably expressed in the majority and dissenting opinions in the Slaughter-House Cases (1873), it has always been common ground that this Clause protects the third component of the right to travel. Writing for the majority in the Slaughter-House Cases, Justice Miller explained that one of the privileges conferred by this Clause “is that a citizen of the United States can, of his own volition, become a citizen of any State of the Union by a bona fide residence therein, with the same rights as other citizens of that State.”

Justice Samuel Freeman Miller had written in the Slaughter-House Cases that the right to become a citizen of a state by residing in the state “is conferred by the very article under consideration.”^[12]