Every ten years, after the census, states redraw congressional and state legislative districts. Most states task their legislatures with this; a growing minority use independent or bipartisan commissions. Computer-aided drawing has made partisan gerrymandering far more precise — districts can be optimized to "pack" opposition voters into a few districts and "crack" them across many others.
The Supreme Court ruled in Rucho v. Common Cause (2019) that partisan gerrymandering is non-justiciable in federal courts, leaving the issue to states. Racial gerrymandering remains justiciable under the Voting Rights Act and the 14th Amendment.
Reform proposals include independent redistricting commissions, mathematical fairness criteria (compactness, partisan symmetry), and federal legislation to set national standards.