Leaders of the Appropriations Committee are trying to tighten up funding legislation to give the Trump administration less leeway to refuse to spend federal money.
Senator Patty Murray of Washington joined other Appropriations Committee members in a letter to Russell T. Vought, the director of the White House Office of Management and Budget, to protest his decision to not spend nearly $3 billion in emergency funds.
Many state delegations are already under single-party control. New maps could tighten the partisan grip while decreasing the importance of general elections.
Gene Karpinski, who retired from leading the League of Conservation Voters after two decades, said the group that once backed G.O.P. candidates now finds it difficult to do so.