38 UNITED STATES V. MOHAMUD the United States government learned that Mohamud was in contact with that foreign national, who was located overseas. This contact—a limited number of emails between Mohamud and the foreign national—was used to obtain a FISA warrant to surveil Mohamud and his activities. None of these emails was introduced at trial.21 We permitted the parties to file supplemental briefs to address the facts offered in the postargument disclosure. a. No Warrant Required to Intercept Overseas Foreign National’s Communications or to Intercept U.S. Person’s Communications Incidentally As a threshold matter, “the Fourth Amendment does not apply to searches and seizures by the United States against a non-resident alien in a foreign country.” United States v. 21 We address only Mohamud’s as-applied challenge. See United States v. Salerno, 481 U.S. 739, 745 (1987) (“A facial challenge to a legislative Act is, of course, the most difficult challenge to mount successfully, since the challenger must establish that no set of circumstances exists under which the Act would be valid.”). Though he also purports to challenge § 702 facially, citing City of Los Angeles v. Patel, 135 S. Ct. 2443, 2451 (2015), Mohamud does not explain why techniques not employed in this case would require suppression of the evidence gathered here. We do not read Patel to permit courts, in a criminal prosecution, to suppress evidence based on a Fourth Amendment challenge to techniques not employed in a particular case. See, e.g., United States v. Posey, 864 F.2d 1487, 1491 (9th Cir. 1989) (“[W]e think it clear that appellant may not make a facial challenge to the FISA without arguing that the particular surveillance against him violated the Fourth Amendment. . . . Even if he is correct that the FISA’s language might be applied in ways that violate the Fourth Amendment, he must show that the particular search in his case violated the Fourth Amendment. Appellant cannot invalidate his own conviction on the argument that others’ rights are threatened by FISA.” (emphasis in original)).