Republican lawmakers are pursuing the unusual mid-decade redistricting plan amid pressure from President Donald Trump to protect the GOP’s slim majority in the U.S. House.

Texas Democratic lawmakers left two weeks ago to block a GOP plan to redraw the state’s congressional districts. They said they were returning now that California Democrats are adopting a counterproposal.

The gambit has triggered a national redistricting war, as governors from both major parties threaten to initiate similar efforts in other states.