Cite as: 600 U. S. ____ (2023) 9 THOMAS, J., dissenting Harper III did not “alter or amend in any way the judgment in Harper I,” ante, at 9, is both irrelevant and incorrect. It is irrelevant because our jurisdiction requires a case, and this case is over no matter what becomes of the empty husk of Harper I ’s interlocutory judgment. It is incorrect because Harper I ’s judgment—reversing the trial court’s original judgment and remanding the case—was completely negated by Harper III ’s affirmance of the same trial-court judgment. In the same vein, the majority’s suggestion that Harper I has any “res judicata consequences” is completely inapposite. Ante, at 9 (internal quotation marks omitted). Res judicata is the principle that “[a] final judgment on the merits of an action” bars relitigation “in [a] second action” of the same claim or of issues actually litigated and necessary to the judgment in the first action. Federated Department Stores, Inc. v. Moitie, 452 U. S. 394, 398 (1981); see also Taylor v. Sturgell, 553 U. S. 880, 892 (2008). Harper I was not a final judgment (as the majority concedes by applying Cox Broadcasting), so res judicata simply has nothing to do with it. Nothing decided by Harper I was res judicata in the second state-court appeal, see Southern R. Co. v. Clift, 260 U. S. 316, 319 (1922), nor would Harper I ’s interlocutory Elections Clause holding have any res judicata effect in a future action between these parties, see Restatement (Second) of Judgments §27, and Comment h, and Illus. 13 and 14 (1980) (only issue determinations essential to a final —————— regarding redistricting of congressional districts.” Id., at ___, 886 S. E. 2d, at 419. To the extent that Harper III suggests any view about whether such provisions would be binding if they existed, it seems to suggest agreement with petitioners. See ibid. (“The Federal Constitution . . . commits drawing of congressional districts to the state legislatures subject to oversight by the Congress of the United States”). But, of course, Harper III had no need to decide that question, because its statelaw justiciability holding fully determined the judgment in this action, thus mooting petitioners’ alternative Elections Clause defense.