In Ms. Cisneros’s campaign, he sees an identity-first approach, in which she casually toggles between English and Spanish, speaks of identifying with South Texas and its struggles, contrasts that to the outsiders in Washington, then pivots to issues like health care and reproductive rights.After the Trump shake-up, the region could be ready for a new approach, said Cecilia Ballí, an anthropologist and researcher at the University of Houston who did extensive interviews in South Texas after Mr. Trump’s 2020 gains. For decades, the region has been run by insular political families like Mr. Cuellar’s. His brother is the sheriff of Laredo’s Webb County; his sister is a former municipal judge and tax collector there.Ms. Ballí said that with no real competition between the parties, Democrats have won loyalty with rallies and free food, but no emphasis on issues or retail politics. Mr. Trump’s brand of personality-driven, outsider bombast broke through to many disillusioned Hispanic voters.Ms. Cisneros agreed: “They’ve been voting Democrat for such a long time, and obviously, the poverty rate hasn’t gone down, the uninsurance rate hasn’t gone down. People still have to work two or three jobs just to make ends meet,” she said. Add the pandemic and a shutdown of border crossings that crippled Laredo commerce, “and I think that just led to the perfect storm.”Mr. Cuellar has weapons of his own: an unrivaled network of backers in the political establishment and a seat on the House Appropriations Committee, from which he has plied the sprawling district with federal largess, from $45,520,000 in transportation projects for Atascosa County in the district’s north to $15,142,000 for cattle health in Zapata County in the south.Then there are the fears that a Cisneros victory March 1 would hand newly confident Republicans the seat. Ms. Cisneros insists that she is the answer to the Republican rise, an outsider voice to give hope to the region’s frustrations. Redistricting changes actually made the 28th slightly more Democratic, with more voters from San Antonio’s Bexar County, a potential boon to Ms. Cisneros’s chances — on Tuesday and in November. The district shifted from 76.9 percent Hispanic to 75.3 percent, but a slight rise in Anglo voters could actually help Ms. Cisneros if those new voters are San Antonio liberals.But Mr. Cuellar beat his Republican challenger handily in 2020, with 58 percent of the vote, while Mr. Biden eked out 51.5 percent. Those Trump-Cuellar voters could move to the Republican House candidate that emerges from the seven-candidate primary.