Nearly a half-century ago, Congress decided that the government could not end racial discrimination in voting simply by suing one state, county, or city at a time, because officials who were determined to keep minorities away from the polls were quickly shifting to new tactics. The only way to keep ahead of those tactics, Congress decided, was to bar the worst offenders among state and local governments from adopting any new election laws until they had first proved they would not discriminate. That was a massive shift in policy, and it worked: the law that Congress passed in 1965, the Voting Rights Act, is now widely credited as the most effective civil rights law in American history; even the Supreme Court has said so. But the Supreme Court has grown to be one of the skeptics about the constitutionality of the law, partly because of the very fact that the law has been so successful. ”Things have changed in the South,” the Court commented three years ago. And, at that time, it pondered striking down the key part of the 1965 law — Section 5 — on the theory that “the evil that Section 5 is meant to address may no longer be concentrated” in the states, counties, and cities that must obey that section. There are nine of those states, plus local governments in seven other states, that must get permission in Washington before they may change any law dealing with voting — no matter how trivial the change. The Court chose in 2009 to leave the law as is, but hinted that Congress should update it.