The small minority of Republicans who derailed the vote to renew the Voting Rights Act of 1965 are in danger of being portrayed as members of the “Know Nothing” Party of the 1850s, whose hypocrisy President Lincoln said he could never stomach. These were nativists who disdained Catholics and immigrants while dismissing African-Americans as three-fifths of a human being. When asked about their party’s position, they would reply: “I know nothing.”

Today’s opponents of renewal of the Voting Rights Act either truly don’t know, misunderstand or, worse, purposely misstate the purpose and effect of the Voting Rights Act.

Opponents criticize parts of the act that require jurisdictions with a long and pervasive history of voting discrimination against racial and ethnic minorities to obtain federal pre-approval for voting changes. They claim that this requirement is too burdensome and no longer needed.

Burdensome? Only for jurisdictions that continue to discriminate. To date, every jurisdiction since 1982 that has petitioned to be released from Justice Department oversight, demonstrating that they no longer discriminate, has had their request granted. In fact, the state of Virginia has had nine counties and three cities exempted in the last several years.

But the facts clearly demonstrate that this protection is still needed.

Take the example of Kilmichael, Miss. In 2001, the all-white town council decided abruptly to cancel municipal elections when it became clear that, for the first time in town history, a significant number of African-American candidates qualified for the election. After review, the Department of Justice concluded that canceling the election was an attempt to suppress African-American candidates and ruled that the election go on as planned.

Obstructionists of renewal often cite the very success of the Voting Rights Act — the increased number of minority voters and legislators — as a sign that the law is no longer needed and should be weakened or done away with. They forget the 200 years of discrimination and disenfranchisement that made the Voting Rights Act necessary and the progress that has been made in the last 40 years toward ending voting discrimination because of its existence.The fact that it has been so successful is one of the arguments in favor of its extension in 2007.

Why not update the law, some say, to key coverage to modern-day registration and turnout numbers? Answer: That would be confusing the symptom with the disease. In 1965, Congress used registration and turnout data to select which states should be subject to federal pre-approval of voting changes because that was the way to best identify those places with the longest and worst history of voter disfranchisement and entrenched discrimination by recalcitrant jurisdictions. Congress understood that while the formula for identifying the worst actors could be designed this way, the test for graduating from federal oversight was keyed to whether the discrimination had ended.

One part of the act requires that voting information or assistance be provided to citizens who don’t speak or read English very well, allowing them to cast an informed ballot. This is not an issue about immigration. More than 70% of people who use language assistance to vote are native-born. As for the others, why should the quality of a person’s English language skills determine whether they can enjoy the most fundamental and basic right of our democracy — the right to vote?

Far from dividing America, the Voting Rights Act assures that racial and ethnic minorities have an equal opportunity to elect candidates who reflect their views and values, ensuring the nation’s continued progress toward a society where race ultimately will no longer matter.

Our nation is a far different place today from what it was in 1965. Discriminatory practices such as poll taxes, literacy tests, violence and intimidation to keep minorities from voting no longer pervade communities as they once did. But the continuing well-documented efforts of elected officials to dilute minority voting strength and deter minority political participation strongly supports renewal of the Voting Rights Act.

The Party of Lincoln should not allow itself to be captured by regressive forces. Nor should it bog itself down in a debate about which political party is advantaged by ending voter discrimination. Rather, we should all join to ensure that every American citizen have an equal opportunity to vote and that every vote be counted.

Mr. Kemp is founder and chairman of Kemp Partners.