THE 1965 VOTING RIGHTS ACT remains one of this country’s foremost accomplishments. Constitutional amendments following the Civil War barred states and localities from abridging the right to vote on the basis of race, yet for the better part of a century, white racists managed to stay a step ahead of the federal government’s enforcement of these protections. The Voting Rights Act was designed to stamp out the varied and shifting strategies local officials used to prevent African Americans from voting.

On Wednesday the Supreme Court will consider whether the Voting Rights Act has worked so well that its toughest rules have now outlived their time.

Provisions of the act require certain states and localities with a history of discrimination to clear any proposed change in voting rules with the federal government. Shelby County, Alabama, claims that immense progress since 1965 in rooting out official discrimination renders pre-clearance an unwarranted burden on those jurisdictions that must comply, unjustifiably subjecting some states to unequal treatment and violating their constitutional prerogative to regulate elections within their borders.

The rate at which the Justice Department has been objecting to changes in voting rules, the county’s lawyers point out, has plummeted since the 1960s. The formula Congress used to sort out which states are subject to pre-clearance and which aren’t, they say, is out of date. It would be better to allow only after-the-fact lawsuits against discriminatory behavior under a different section of the act, which applies to the whole country.

Backers of pre-clearance agree that there’s been progress, but they argue that the act’s task is incomplete. They point out that Congress reauthorized the law in 2006 based on a voluminous record of recent efforts by pre-clearance jurisdictions to institute discriminatory voting rules. The NAACP Legal Defense and Educational Fundargues that voting dilution — for example, when officials slice and dice minority populations into myriad districts to limit their electoral influence — is “an old poison in new bottles.” Even if the Justice Department is objecting less, protecting the right to vote is of such importance that Congress should have the authority to use strong measures to protect it.

Pre-clearance jurisdictions on the whole still have a worse record than those not covered. Per capita, they have seen many more successful after-the-fact legal challenges to their voting rules. Pre-clearance advocates look at these figures and rightly wonder how much worse they would be if the pre-clearance procedure did not exist. Besides, the law allows jurisdictions to escape the pre-clearance requirement after a decade of good behavior — a crucial element of the act that allows for real-time adjustment of its rough geographic distinctions.

In reauthorizing the Voting Rights Act seven years ago, a bipartisan majority of lawmakers — 390 to 33 in the House, 98 to 0 in the Senate — determined that the evidence justified maintaining pre-clearance. Shelby County and its allies have not given the high court reason enough to repudiate Congress’s resounding judgment.