The State of Oregon (the state) (plaintiff) legalized assisted suicide through a ballot measure in 1994. Under this law, physicians who dispensed or provided a lethal dose of drugs to terminally ill patients under specific safeguards were immune from civil or criminal liability. These drugs were federally regulated under the Controlled Substances Act (CSA), 21 U.S.C. § 801 et seq. In 2001, U.S. Attorney General John Ashcroft, the predecessor to Alberto Gonzales (defendant), issued an interpretive rule providing that assisted suicide was not a legitimate medical practice and that dispensing or prescribing drugs for that purpose was prohibited by the CSA. The state obtained an injunction in district court to prevent enforcement of the interpretive rule, and the court of appeals held that the interpretive rule was invalid. Gonzales petitioned for certiorari.