The Supreme Court last week heard oral argument in a case challenging the constitutionality of a key provision of the Voting Rights Act.

That law, originally enacted in 1965, and most recently reauthorized in 2006, aims to enforce the guarantees of the Fourteenth and Fifteenth Amendments, which respectively guarantee to all persons the “equal protection of the laws” and provide that “the right to vote shall not be denied or abridged on account of race” by any jurisdiction in the United States.

Such a challenge may seem like a step backwards, but in reality, the fact that the Supreme Court has a difficult decision to make here is a clear indicator of how much progress this country has made toward establishing genuine equality among the races.

In 1965, a full century after the end of the Civil War, several states and other political jurisdictions still systematically excluded African Americans and other minority persons from voting. Those states and communities had, for much of that intervening century, deployed literacy tests, poll taxes and other such devices as weapons to keep minorities from voting and to entrench white supremacy.

When those overtly discriminatory devices were prohibited, racist politicians invented still other techniques for excluding minority voters. They would redraw voting districts or, at the last moment, change the polling place to a place inconvenient, or perhaps even dangerous, for minority voters to approach.

Those measures were very effective. Across a swath of the old Confederacy, and in several places elsewhere, African Americans registered to vote at far lower rates than whites and were politically marginalized.

To solve the problem, the Voting Rights Act created two mechanisms for protecting voting rights. First, it authorized the U.S. Attorney General to bring suits to challenge any violation of voting rights, anywhere in the country. By 1965, this step was long overdue, and it is uncontroversial now.

In 1965, however, it was felt acutely, and at that time, it was demonstrably true, that remedial measures wouldn’t suffice to protect voting rights. Remedial lawsuits take time, and determinedly racist jurisdictions could implement exclusionary policies, then change them for different exclusionary policies, before the Justice Department and the courts could really react to the first one. In the meanwhile, voting rights would have been infringed.

To solve that problem, the Voting Rights Act created a second and much more restrictive pre-emptive enforcement mechanism, that was applied to those jurisdictions that were especially discriminatory in 1964.

Once those jurisdictions had been made to adopt nondiscriminatory laws, they were forbidden from making any changes, large or small, to their voting procedures, without getting approval, in advance, from the U.S. Attorney General.

This “preclearance” provision was recognized at the time as an extraordinary measure, because it imposed a very significant burden on some communities but not others, and because it is an action that interferes directly with the ordinary prerogatives of self-government.

It was originally authorized to last for only five years, and it was expected that in those five years, firm government action would put an end to the most discriminatory practices. Since then, the provision has been reauthorized four more times.

The question before the court now is whether this “preclearance” provision, in its current form, still makes sense today. The gross abuses it was designed to arrest vanished long ago, and it is hard see that there is anything reasonable in punishing some states and communities today based on what was done in 1964.

Today, in some of the covered states in the deep south, blacks vote at a higher rate than whites, while in several other jurisdictions not covered by the “preclearance” requirement, one can find distressingly large shortfalls in minority voter registration and turnout.

On the other hand, some problems clearly remain in the covered jurisdictions, and the particular county bringing the lawsuit seems to have a record that could well justify strict supervision by the national government.

Moreover, the powers granted to Congress by the Reconstruction Amendments are vast and sweeping, and the Court may feel obliged to defer to the judgment of Congress that the “preclearance” provision is needed — even if it wouldn’t come to the same judgment itself.

Whichever way the Court decides regarding the “preclearance” provision, however, there is one point on which both sides agree: The Voting Rights Act has made what Solicitor General Donald Verrilli calls a “huge difference in transforming the culture of blatantly racist vote suppression that characterized parts of this country for a century.”

Joseph R. Reisert is associate professor of American constitutional law and chairman of the department of government at Colby College in Waterville.