What happened

A federal appeals court backed a Republican-drawn Missouri congressional map that could improve the GOP's chances of winning seven of the state's eight House seats. State courts and the U.S. Supreme Court had previously blocked use of the map, and the dispute returned to the Supreme Court.

Republican case

Republican officials argue the legislature had authority to redraw the districts and that changing back after the new map was already used in a primary would create constitutional and administrative problems.

Democratic case

Democrats argue the map is a mid-decade partisan gerrymander designed to dismantle Democratic Rep. Emanuel Cleaver's district and manufacture an additional Republican seat.

Libertarian / Cato case

Cato's longstanding position is that both parties abuse redistricting when they control the process. It favors objective criteria, transparency and structures that reduce politicians' ability to choose their voters.

Where the disagreement really is

Beyond the immediate legal question, the larger dispute is whether elected officials should be able to redraw districts between censuses primarily for partisan advantage.