In Texas, where last week a federal judge struck down what she called the most restrictive voter ID law in the country, there were two convictions for in-person voter impersonation in one 10-year period. During that time, 20 million votes were cast. Nor is there any evidence that these laws encourage more voters to come to the polls. Instead, in at least two states — Kansas and Tennessee — they appear to have reduced turnout by 2 percent to 3 percent, according to a report released last week by the Government Accountability Office.

Voter ID laws, as their supporters know, do only one thing very well: They keep otherwise eligible voters away from the polls. In most cases, this means voters who are poor, often minorities, and who don’t have the necessary documents or the money or time to get photo IDs.

In her remarkable 143-page opinion in the Texas case, Federal District Judge Nelva Gonzales Ramos found that the law violated both the Equal Protection Clause and the Voting Rights Act, and that by forcing registered voters to track down and pay for qualifying documents, it functioned as an “unconstitutional poll tax.”

Most striking of all, Judge Ramos found that the rapid growth of Texas’s Latino and black population, and the state’s “uncontroverted and shameful history” of discriminatory voting practices — including whites-only primaries, literacy restrictions and actual poll taxes — led to a clear conclusion: Republican lawmakers knew the law would drive down turnout among minority voters, who lean Democratic, and they passed it at least in part for that reason. Judge Ramos’s finding of intentional discrimination is important because it could force Texas back under federal voting supervision, meaning changes to state voting practices would have to be preapproved by the federal government. (Texas appealed the ruling; a federal appeals court is now considering whether to put it on hold until after the election.)

Eventually the issue will be back before the Supreme Court, which last reviewed a voter ID law in 2008, when it upheld an Indiana law because there was no clear evidence showing how it would harm voters. Thanks to the work of voting-rights advocates and the extraordinarily thorough rulings of Judge Ramos and Judge Lynn Adelman, who struck down Wisconsin’s law, the evidence is in.