How have courts interpreted the rule of causation in cases involving multiple defendants?

In Selzer v. Fleisher, 629 F.2d 809 (2d Cir.1980), a multiple-defendant case, we held that the question of whether the adverse employment decision would have been made absent the protected conduct is "applicable to each defendant separately and cannot be satisfied by a finding as to the defendants collectively." Id. at 814. This rule of causation allows an individual defendant to escape personal liability by proving a legitimate alternative motive for his vote. Furthermore, if a majority of defendants prove that their individual votes against the plaintiff would have been the same irrespective of the plaintiff's protected conduct, then the defendants as a group cannot be held liable, and no individual defendant, even one whose proof falls short, can be so held because causation is absent. See id. at 814 n. 1 (Kaufman, J., concurring in part and dissenting in part).