Numerous times since the civil rights era, courts have struck down how partisan state legislatures set up legislative districts on the grounds that those decisions diminished the political power of racial minorities. But courts have been far less likely to intervene in cases where states organized voting districts to boost one party, preferring to not get involved in explicitly political matters.

On Monday, a federal district court struck down Wisconsin’s state legislative districts, saying they were unconstitutionally gerrymandered to favor Republicans. The ruling is the first in three decades — and the second in the nation’s history — to strike down a district plan on partisan, rather than racial, grounds. And if other courts follow suit, the design of state legislative districts in more than a dozen other states could meet a similar fate.

Numerous times since the civil rights era, courts have struck down how partisan state legislatures set up legislative districts on the grounds that those decisions diminished the political power of racial minorities. But courts have been far less likely to intervene in cases where states organized voting districts to boost one party, preferring to not get involved in explicitly political matters.

This was why the decision Monday by the federal District Court for the Western District of Wisconsin was so significant. The court found that the Republican-held legislature had intentionally manipulated district lines to favor Republican candidates. And that manipulation was so extreme, it found, that it violated the “one person, one vote” principle and the Democratic voters’ rights to fair representation required by the Constitution's promises of equal protection.

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