What Is Gerrymandering, and How Does It Shape the US Congress?

The race for control of the US Congress is not decided by votes alone. Before voters reach the ballot box, the boundaries of electoral districts can influence which party is best placed to win seats.

Gerrymandering is the manipulation of those boundaries to give a political party or group an advantage. By placing some voters in one district and others elsewhere, mapmakers can reshape electoral competition without changing anyone’s political preferences.

Two common methods are known as “packing” and “cracking.” Packing concentrates an opponent’s supporters in a limited number of districts, while cracking divides them across several districts to weaken their voting strength.

This matters for the House of Representatives, where members are elected from districts within states. It does not apply in the same way to the Senate, whose members are elected statewide.

Redrawing districts is a routine part of accounting for population changes, but gerrymandering turns that process into a tool for political advantage. The result can be a congressional map that helps a party secure a larger share of seats than its overall support might suggest.