As Texas Republicans move ahead with redistricting to protect or even expand the GOP’s slim majority in the US House, Democratic-run states, led by California, are pushing forward with their own efforts to draw new maps and add Democratic seats.

Texas Republicans are planning to escalate their efforts to end a weeklong holdout by Democrats if they don’t return to the state Capitol to face a vote on new congressional voting maps.

As a Texas senator summoned the F.B.I. to round up Democrats, the redistricting war that began in Texas was spreading, with California aiming at five Republican House seats.