563 U.S. ___ (2011). There the District Court found that the defendant state officers had violated the Fourth Amendment, but rendered judgment in their favor because they were entitled to official immunity, application of the Fourth Amendment to their conduct not having been clear at the time of violation. The officers sought to appeal the holding of Fourth Amendment violation, which would circumscribe their future conduct; the plaintiff continued to insist that a Fourth Amendment violation had occurred. The "prudential" discretion to which both those cases refer was the discretion to deny an appeal even when a live controversy exists—not the discretion to grant one when it does not. The majority can cite no case in which this Court entertained an appeal in which both parties urged us to affirm the judgment below. And that is because the existence of a controversy is not a "prudential" requirement that we have invented, but an essential element of an Article III case or controversy. The majority's notion that a case between friendly parties can be entertained so long as "adversarial presentation of the issues is assured by the participation of amici curiae prepared to defend with vigor" the other side of the issue, ante, at 10, effects a breathtaking revolution in our Article III jurisprudence.
It may be argued that if what we say is true some Presidential determinations that statutes are unconstitutional will not be subject to our review. That is as it should be, when both the President and the plaintiff agree that the statute is unconstitutional. Where the Executive is enforcing an unconstitutional law, suit will of course lie; but if, in that suit, the Executive admits the unconstitutionality of the law, the litigation should end in an order or a consent decree enjoining enforcement. This suit saw the light of day only because the President enforced the Act (and thus gave Windsor standing to sue) even though he believed it unconstitutional. He could have equally chosen (more appropriately, some would say) neither to enforce
