The Sun Belt is looking purple

The texture of the midterm results has changed most starkly over the last week in the West, as slow-counting states like Arizona and California have tallied their ballots. Democrats have captured Republican-held Senate seats in Nevada and Arizona, partially offsetting their losses in the heavily white, conservative states where Republicans unseated Democratic senators.

And in California, what looked like a night of incremental Democratic gains has turned into a slow-motion rout for the G.O.P. Republicans are on track to lose between four and seven seats there, chiefly in the suburbs of Southern California, where even Representative Dana Rohrabacher, a 30-year incumbent, went down in defeat.

Further down the ballot, there were signs of Democratic gains in historically Republican parts of the Southwest: In Arizona, where Republicans have dominated state politics, Democrats also captured the office of education superintendent, and a second important statewide election — for secretary of state — was still too close to call a week into the count. In Nevada, where Democrats had not won a governor’s race since 1994, they captured the governorship and the offices of lieutenant governor, attorney general, state treasurer and state controller.

In Texas, Democrats gained at least a dozen seats in the Statehouse and, despite partisan gerrymandering, picked up two congressional seats. Five Republican congressional candidates there who were strongly favored to win ultimately prevailed with less than 52 percent of the vote.

Texas and Arizona are unlikely to be blue states anytime soon, but after years of tilting at the Southwest with little to show for it, Democrats saw real signs that the region is becoming a battleground.

Grant Woods, a former Republican state attorney general in Arizona who recently registered as a Democrat, said Mr. Trump and the Republican Party had moved too far right for voters in the Southwest. Mr. Woods, who is considering a run for Senate in 2020, said the midterm results were encouraging.