A federal appeals court that already has said private individuals and groups cannot sue under a key part of the federal Voting Rights Act went even further Wednesday toward blocking lawsuits over alleged racial bias in voting in seven Midwest states. The latest ruling reversed a legal victory for two tribal nations in North Dakota that challenged a legislative redistricting plan. The ruling shuts off a route to Section 2 of the Voting Rights Act through a federal civil rights law known as Section 1983, which allows people to sue state officials to vindicate their federal or constitutional rights, said Jonathan Topaz, staff attorney for the American Civil Liberties Union Voting Rights Project.