Scotusblog’s eye-witness reporter in the U.S. Supreme Court oral argument (in Shelby County, Alabama v Holder) predicts that five justices of the U.S. Supreme Court will vote to invalidate the coverage formula for section 5 of the federal Voting Rights Act. If this happens, Congress would be faced with the question of whether to write a new coverage formula. If Congress did nothing, then presumably Section 5 could no longer be enforced. Section five of the Voting Rights Act is the part of the Act that requires certain states and local jurisdictions to get permission from the federal government before changing any election law or practice.
UPDATE: here is the transcript.