Anxious House Members Learn Their Peril Today With Census Data

House members dread years ending in “2,” when new congressional maps are implemented. It’s time to start sweating again, as the line-drawing process begins now.

The Census Bureau’s release Thursday of in-depth population data means state legislatures and redistricting commissions can begin crafting new district lines to be used for the next decade. Many House members will have to run in unfamiliar terrain, putting them at risk of losing their seats in either the primary or the general election.

With Democrats protecting a five-seat House majority and Republicans in charge of redrawing more congressional maps, both parties are likely to ...