How widespread must an injury to a State's quasi-sovereign interest be, and how clearly must it transcend harm to particular private parties, to give the State parens patriae standing?

Ordinarily, litigants are not permitted to sue in federal court to vindicate the rights of third parties. Parens patriae standing, whereby a State may sue on behalf of its residents to remedy harms that they have suffered, is an exception to that rule. And it is a potent one that has become a favorite of state attorneys general looking to unleash their governments’ resources against all manner of supposed wrongdoers: corporations, other States, and more. This Court in Alfred L. Snapp & Son, Inc. v. Puerto Rico ex rel. Barez , 458 U.S. 592 (1982) articulated elements that a State must satisfy in order to wield that powerful tool. The State “must express a quasi-sovereign interest”: an “interest[] that the State has in the wellbeing of its populace.” Id. at 602, 607. Further, the State must allege an injury to that interest that affects “a sufficiently substantial segment of its population” and that transcends mere harm to those “particular private parties” themselves. Id. at 607. The question presented, which a Judge below observed has generated such “confusion among the Courts of Appeals” as to warrant “clarification or correction by the Supreme Court,” is: How widespread must an injury to a State’s quasi-sovereign interest be, and how clearly must it transcend harm to particular private parties, to give the State parens patriae standing?