For the first time since the Supreme Court junked a core provision of the Voting Rights Act in June, a federal court has used the strongest surviving part of the act to strike down a state’s voter-identification law, and, in the process, has set out a detailed road map for upcoming challenges to similar laws around the country.

Supporters of these laws insist they are necessary to prevent fraud at the polls, though such fraud is basically nonexistent. The real point is to deter from the polls significant numbers of Democratic voters, particularly minorities and the poor.

That was the heart of the reasoning by Judge Lynn Adelman of Federal District Court in Milwaukee, who issued an extraordinarily thorough 90-page ruling on Tuesday invalidating Wisconsin’s voter-ID law as a harmful solution in search of an imaginary problem. The law was passed by a Republican-controlled statehouse in 2011 and required that a prospective voter present a government-issued photo ID, like a driver’s license or passport.

“Virtually no voter impersonation occurs in Wisconsin, and it is exceedingly unlikely that voter impersonation will become a problem in Wisconsin in the foreseeable future,” the judge wrote.