8 COOPER v. HARRIS Opinion of the Court Carolina makes two related arguments based on the Dick­ son litigation: first, that the state trial court’s judgment should have barred this case altogether, under familiar principles of claim and issue preclusion; and second, that the state court’s conclusions should cause us to conduct a “searching review” of the decision below, rather than deferring (as usual) to its factual findings. Reply Brief 6. The State’s preclusion theory rests on an assertion about how the plaintiffs in the two cases are affiliated. As the State acknowledges, one person’s lawsuit generally does not bar another’s, no matter how similar they are in substance. See Taylor v. Sturgell, 553 U. S. 880, 892–893 (2008) (noting the “deep-rooted historic tradition that everyone should have his own day in court”). But when plaintiffs in two cases have a special relationship, a judgment against one can indeed bind both. See id., at 893– 895 (describing six categories of qualifying relationships). The State contends that Harris and Bowser, the plaintiffs here, are members of organizations that were plaintiffs in Dickson. And according to North Carolina, that connection prevents the pair from raising anew the questions that the state court previously resolved against those groups. See Brief for Appellants 20–21. But North Carolina never satisfied the District Court that the alleged affiliation really existed. When the State argued that its preclusion theory entitled it to summary judgment, Harris and Bowser responded that they were not members of any of the organizations that had brought the Dickson suit. See 3 Record 1577–1582 (Defs. Motion for Summary Judgment); 4 Record 101–106 (Pls. Opposition to Motion for Summary Judgment). The parties’ dueling contentions turned on intricate issues about those groups’ membership policies (e.g., could Harris’s payment of dues to the national NAACP, or Bowser’s financial contribution to the Mecklenburg County NAACP, have made either a member of the state branch?). Because of