California Democrats are rushing to schedule an election to remake U.S. House districts to counter plans to boost Republican seats in Texas.

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.

Texas has been the epicenter of Trump’s push to gerrymander congressional maps to shore up Republicans’ narrow House majority before next year. But the standoff is threatening to into other states — including California.