in United States v. Palomar-Santiago the Court held that defendants charged with unlawfully reentering the United States following an order of removal can collaterally attack the validity of the prior removal order only when three statutory prerequisites are met.
In Guam v. United States, the Court addressed the trigger for a contribution action under § 113(f)(3)(B) in the common context of a government settlement that does not specify the resolution of CERCLA liability.