what is reapportionment and when does it take place
Apportionment (politics) 2 U.S.C. § 2a, based on the Reapportionment Act of 1929, reapportions the Representatives to the states following each decennial census. It left the states to decide how and whether to redistrict, except in the case that the census changes the state's number of Representatives, but federal court cases now require states to redistrict based on each census.
Warren Court In the key apportionment case Reynolds v. Sims (1964)[23]  Warren delivered a civics lesson: "To the extent that a citizen's right to vote is debased, he is that much less a citizen," Warren declared. "The weight of a citizen's vote cannot be made to depend on where he lives. This is the clear and strong command of our Constitution's Equal Protection Clause." Unlike the desegregation cases, in this instance, the Court ordered immediate action, and despite loud outcries from rural legislators, Congress failed to reach the two-thirds needed pass a constitutional amendment. The states complied, reapportioned their legislatures quickly and with minimal troubles. Numerous commentators have concluded reapportionment was the Warren Court's great "success" story.[24]