U.S. House members and state representatives are elected by district. Those districts are updated each decade after the census in a process known as redistricting. Redistricting can alter the shape and composition of a district. Often, the political party in power creates or redraws districts to maximize its advantage. This process is commonly known as partisan gerrymandering. It decreases electoral competition. New mapping technologies have enabled political parties to manipulate district lines even more effectively in their favor. Boundaries can be engineered down to the block or household level. The Supreme Court has allowed partisan gerrymandering. In 2018, the Supreme Court allowed North Carolina, Wisconsin, and Maryland to draw maps in favor of one political party. The Court did not, however, rule on whether partisan gerrymandering is legal.
To address partisan gerrymandering, states such as Arizona, Iowa, and California have used independent nonpartisan or bipartisan commissions to lead redistricting efforts. These commissions draw districts based on communities of shared interest. They do not consider incumbency or party affiliation when doing so. The resulting legislative districts are compact, contiguous, and reflective of their communities. These processes also increase the number of competitive districts.
Legislators also have tried to dilute the voting power of certain racial and ethnic groups through redistricting. This is known as racial gerrymandering. This practice is illegal under the Voting Rights Act. However, the Supreme Court has allowed certain practices that some argue constitute racial gerrymandering. In 2017, the Supreme Court blocked North Carolina’s entire congressional district map. It ruled the map was illegally racially gerrymandered. However, in a similar case in 2018, the Court allowed most of the redistricting in Texas, which some had argued was racially gerrymandered. The Court only blocked one particularly race-based Texas legislative district.