Opinion of Gorsuch, J.
“common law” path and the Court fails to supply guidance on how to resolve any of them.
Right out of the gate, lower courts will have to decide between two very different approaches. One option is to defer to the Executive Branch’s judgment on whether to grant immunity to a foreign sovereign—an approach sometimes employed by federal courts in the years immediately preceding the FSIA’s adoption. The other option is for a court to make the immunity decision looking to customary international law and other sources. Compare Brief for United States 21–26 with Brief for Professor Ingrid (Wuerth) Brunk et al. as Amici Curiae 6–25.
Whichever path a court chooses, more questions will follow. The first option—deferring to the Executive—would seem to sound in separation-of-powers concerns. But does this mean that courts should not be involved in making immunity determinations at all? And what about the fact that the strong deference cases didn’t appear until the 20th century; were courts acting unconstitutionally before then? If not, should we be concerned that deference to the Executive’s immunity decisions risks relegating courts to the status of potted plants, inconsistent with their duty to say what the law is in the cases that come before them? See, e.g., Brief for Professor Ingrid (Wuerth) Brunk et al. as Amici Curiae 17–21.
The second option—applying customary international law—comes with its own puzzles. If the briefing before us proves anything, it is that customary international law supplies no easy answer to the question whether a foreign sovereign enjoys immunity from criminal prosecution. Compare Brief for Professor Roger O’Keefe as Amicus Curiae 11–16 with Brief for Mark B. Feldman et al. as Amici Curiae 12–13. Nor is it even altogether clear on what authority federal courts might develop and apply customary international law. Article VI of the Constitution does not list
