The Voting Rights Act that goes on trial at the Supreme Court on Wednesday has helped boost African Americans' presence in Southern legislatures. But in a twist of irony, it also has contributed to their loss of political clout.

Since its passage in 1965, the law's Section 5 has forced states with a history of racial discrimination to clear changes in voting procedures with the federal government. The Justice Department, in turn, has insisted that drawing district lines is one of those procedures – one that should give blacks and other minorities ample opportunity to elect their preferred candidates.

That has led to the creation of so-called majority-minority election districts dominated by blacks or Hispanics, nearly all of them Democrats. Achieving that goal, however, has required the simultaneous creation of more heavily white, Republican districts in surrounding areas.

Although the Voting Rights Act has played a major role in the South's racial transformation, it also has played a supporting role in its political transformation. In 1965, every state legislature was Democratic. In 2013, they are all Republican.

"African Americans are totally and completely shut out of any political influence, with a few exceptions, in the Southern states," says David Bositis, senior research associate at the Joint Center for Political and Economic Studies.

Read more at USA Today.