WASHINGTON -- A deeply divided Supreme Court threw out the most powerful part of the landmark Voting Rights Act on Tuesday, a decision deplored by the White House but cheered by mostly Southern states now free from nearly 50 years of intense federal oversight of their elections.Split along ideological and partisan lines, the justices voted 5-4 to strip the government of its most potent tool to stop voting bias -- the requirement in the Voting Rights Act that all or parts of 15 states with a history of discrimination in voting, mainly in the South, get Washington's approval before changing the way they hold elections.Chief Justice John Roberts, writing for a majority of conservative, Republican-appointed justices, said the law's provision that determines which states are covered is unconstitutional because it relies on 40-year-old data and does not account for racial progress and other changes in U.S. society.The decision effectively puts an end to the advance approval requirement that has been used to open up polling places to minority voters in the nearly half century since it was first enacted in 1965, unless Congress can come up with a new formula that Roberts said meets "current conditions" in the United States. That seems unlikely to happen any time soon.President Obama, the nation's first black chief executive, issued a statement saying he was "deeply disappointed" with the ruling and calling on Congress to update the law.But in the South, Alabama Gov. Robert Bentley said that while the requirement was necessary in the 1960s, that was no longer the case. He said, "We have long lived up to what happened then, and we have made sure it's not going to happen again."The advance approval, or preclearance, requirement shifted the legal burden and required governments that were covered to demonstrate that their proposed election changes would not discriminate.Going forward, the outcome alters the calculus of passing election-related legislation in the affected states and local jurisdictions. The threat of an objection from Washington has hung over such proposals for nearly a half-century. Unless Congress acts, that deterrent now is gone.That prospect has upset civil-rights groups which especially worry that changes on the local level might not get the same scrutiny as the actions of state legislatures.Tuesday's decision means that a host of state and local laws that have not received Justice Department approval or have not yet been submitted can take effect. Prominent among those are voter identification laws in Alabama and Mississippi.Texas Attorney General Greg Abbott, a Republican, said his state's voter ID law, which a panel of federal judges blocked as discriminatory, also would be allowed to take effect.Justice Ruth Bader Ginsburg, dissenting from the ruling along with the court's three other liberal, Democratic appointees, said there was no mistaking the court's action."Hubris is a fit word for today's demolition" of the law, she said.Reaction to the ruling from elected officials generally divided along partisan lines.Mississippi Lt. Gov. Tate Reeves, a Republican, said in a news release, "The practice of preclearance unfairly applied to certain states should be eliminated in recognition of the progress Mississippi has made over the past 48 years."But Democratic Rep. Bennie Thompson, the only black lawmaker in Mississippi's congressional delegation, said the ruling "guts the most critical portion of the most important civil-rights legislation of our time."Alabama's Bentley, a Republican, pointed to his state's legislature -- 27 percent black, similar to Alabama's overall population -- as a sign of the state's progress.The court challenge came from Shelby County, Ala., a Birmingham suburb.The prior-approval requirement had applied to the states of Alabama, Alaska, Arizona, Georgia, Louisiana, Mississippi, South Carolina, Texas and Virginia. It also covered certain counties in California, Florida, New York, North Carolina and South Dakota and some local jurisdictions in Michigan. Coverage was triggered by past discrimination not only against blacks, but also against American Indians, Asian-Americans, Alaska Natives and Hispanics.Obama, whose historic election was a subtext in the court's consideration of the case, pledged that his administration would continue to fight discrimination in voting. "While today's decision is a setback, it doesn't represent the end of our efforts to end voting discrimination," the president said. "I am calling on Congress to pass legislation to ensure every American has equal access to the polls."Congress essentially ignored the court's threat to upend the voting rights law in a similar case four years ago. Roberts said the "failure to act leaves us today with no choice."Congressional Democrats said they are eager to make changes, but Republicans were largely noncommittal.Sen. Charles Schumer, D-N.Y., said he expects Republicans to block efforts to revive the law, even though a Republican-led Congress overwhelmingly approved its latest renewal in 2006 and President George W. Bush signed it into law."As long as Republicans have a majority in the House and Democrats don't have 60 votes in the Senate, there will be no preclearance. It is confounding that after decades of progress on voting rights, which have become part of the American fabric, the Supreme Court would tear it asunder," Schumer said.