restraining arbitrary and potentially vindictive legislation." Id., at 28-29, 101 S.Ct., at 963-964 (citations omitted). "420 FN20. See Richmond v. J A. Croson Co., 488 U.S. 469, 513-514, 109 S.Ct. 706, 732, 102 L.Ed.2d 854 (1989) ("Legislatures are primarily policymaking bodies that promulgate rules to govern