But the Roberts opinion showed no interest in actual data. Nor did it seem to matter that the law was already adapting to current conditions: Every one of the more than 200 jurisdictions that asked to be removed from the preclearance list was successful, because each showed it was not discriminating.

Instead, the court said the coverage formula had to be struck down because it failed to target precisely all areas with voting rights violations in the country.

Mr. Kousser’s study does not solve this problem, in part because there is no easy way to compare discrimination in places that are under a federal microscope with those that are not. But the study provides the most wide-ranging empirical evidence yet that Congress was amply justified in finding that voting discrimination remains concentrated in the covered states and regions. In other words, the tactics may have changed, but the story remains largely the same. Voting discrimination no longer takes the form of literacy tests and poll taxes. Instead, it is embodied in voter-ID laws, the closing of polling places in minority neighborhoods, the elimination of early-voting days and hours, and much more.

The Supreme Court suggested that Congress could fix the law by updating the coverage formula to more closely reflect where violations are occurring today — and a bipartisan bill introduced in 2014 and reintroduced this year has done just that. So far it has gone nowhere because most Republicans oppose it. Even if it were to pass, there is no guarantee it would survive before a Supreme Court that is highly skeptical of any race-conscious efforts to reduce discrimination.

Meanwhile, the Justice Department and private groups are doing what they can to combat the flood of new discriminatory laws with the surviving provisions of the Voting Rights Act. But without preclearance requirements for places with the worst records on racial discrimination, they will always be a few steps behind.