A widening battle to win control of the House is threatening to make Congress more partisan as red and blue states undertake redistricting efforts that could wipe competitive battleground districts off the map.

At the heart of the redistricting battle is Texas, where Gov. Greg Abbott (R-TX) seeks to redraw the congressional map to add five or more GOP seats. California Democrats have pledged to counter Texas’s plan, which they call a political sham, by doing a mid-decade redistricting of their own.