John Roberts warned Congress four years ago when the Supreme Court initially weighed the 2006 extension of the Voting Rights Act. Writing for the majority, the chief justice highlighted concerns about lawmakers using outdated data and lacking adequate justification for subjecting nine states, most in the South, to federal oversight of their election laws and voting procedures.

On Tuesday, Roberts kept his word as a 5-4 majority of the court struck down a key element of the Voting Rights Act. The law calls for states with a history of discrimination in voting to gain “preclearance” from the Justice Department of almost any changes in procedures. Congress has devised a formula for establishing which states must comply with the requirement. That formula is what the court, Roberts again writing for the majority, found flawed, or “based on 40-year-old facts having no relationship to the present day.”

The invitation is there for Congress to update the formula. Yet that isn’t likely to happen in light of the deep divisions. As it is, in reauthorizing the Voting Rights Act, lawmakers, from both parties, dodged revamping the formula to avoid opening old wounds. Better, the consensus rightly was, to push ahead, knowing the formula still is sufficient to the task of protecting voting rights.

Roberts makes much of the “great strides” the country has taken. He notes that black voter turnout exceeds white turnout in a handful of the states initially covered by the act. He cites Philadelphia, Miss., and Selma, Ala., crucial battlegrounds in the civil rights movement now with black mayors.

No question, much progress has been made the past four decades. Such things as literacy tests long have been removed as barriers to voting. Yet the story hardly ends with turnout numbers and election results. As Justice Ruth Bader Ginsburg noted in dissent, the Justice Department has been plenty busy of late overseeing the voting systems of the identified states, contending with what she calls “second-generation barriers,” such as racial gerrymandering and laws requiring at-large elections in places with a large black minority.

Improvement does not mean the problem has been solved, or that the potential for backsliding has been removed. What is so troubling about the majority opinion is its failure to engage fully what Ginsburg exposes — and more, what Congress discovered in reauthorizing the law.

Make no mistake, Congress performed its due diligence, amassing a voluminous record, huge bipartisan majorities in the House (390-33) and Senate (98-0) voting for the renewal. The federal government has been the guarantor of voting rights, and its authority stems from Congress enacting such landmark civil rights legislation. Lawmakers did nothing to warrant such judicial overreach. The country has been ill-served, many Americans now more vulnerable to voting misdeeds.