State legislatures are required to redraw their congressional to redraw their congressional district boundaries whenever
certain events occur. The most common event that triggers the need for redrawing congressional district boundaries is the decennial census conducted by the U.S. Census Bureau. After the census data is released, state legislatures are responsible for adjusting district boundaries to ensure that each district has roughly equal population size.
Additionally, redistricting may also be required if there are significant changes in the population distribution within a state between censuses. This could happen due to population growth or decline, migration patterns, or other demographic shifts.
State legislatures may also choose to redraw district boundaries in response to legal challenges or court orders regarding unfair or discriminatory districting practices. In such cases, the courts may require the state legislature to reformulate their districts to rectify any perceived inequalities or violations of voting rights.
Ultimately, the specific circumstances for redrawing congressional district boundaries can vary between states, as some may have additional requirements or unique processes outlined in their state constitution or statutes.