But reliance only on Section Two would mean a crucial difference in how hard it may be to block a change in voting rules in an area that is currently covered by Section Five. Those jurisdictions, because of their history of discrimination, must prove that any proposed change would not make minority voters worse off.

By contrast, under Section Two, the burden of proof is on a plaintiff to demonstrate in court that a change would prevent minorities from having a fair opportunity to elect representatives of their choice.

“Getting rid of Section Five is not getting rid of voting rights; it would just make voting rights litigation look like normal lawsuits,” said Ilya Shapiro, a legal scholar at the Cato Institute, which filed a friend-of-the-court brief urging the court to strike down Section Five. “It would mean that if the federal government claims people have been harmed, it would have to prove it.”

But J. Gerald Hebert, who formerly handled voting rights litigation for the Justice Department and is now in private practice, said that losing Section Five would be “devastating to protecting voting rights” because the costs of a lawsuit are so steep. Jon Greenbaum, the legal director for the Lawyers’ Committee for Civil Rights Under Law, said it would mean that the bulk of changes that now receive automatic scrutiny by the federal government could take effect without any review, eliminating a deterrent against mischief.

“Section Five makes all the voting changes public and transparent, because when they are submitted for preclearance, the Justice Department will call local folks in the community and get their take on it,” Mr. Greenbaum said. “If you have no Section Five, a lot of stuff will just go under the radar.”