Former President Donald J. Trump’s brand of populism has been widely viewed as an appeal to white voters. But similar grievances have resonated in the Rio Grande Valley in a profound way.BROWNSVILLE, Texas — Mayra Flores, the daughter of Mexican immigrants, has done much of her campaigning in South Texas in Spanish. She has heard one phrase repeatedly from voters as she and other candidates try to become the first Republicans to represent the Rio Grande Valley in Congress.¿Y nosotros?And what about us?“I hear every day that they’re tired — they feel that there is so much attention and help being given to the immigrants,” Ms. Flores said. “The attention’s on all these illegal immigrants, and not on them.”Grievance politics, it turns out, translates.Donald J. Trump’s brand of populism has been widely viewed as an appeal to white voters: Republicans around the country continue to exploit the fear that the left is attacking religious values and wants to replace traditional white American culture with nonwhite multiculturalism. But similar grievances have resonated in the Rio Grande Valley in a profound way, driving the Republican Party’s successes in a Democratic stronghold where Hispanics make up more than 90 percent of the population.The difference is in the type of culture believed to be under assault. Democrats are destroying a Latino culture built around God, family and patriotism, dozens of Hispanic voters and candidates in South Texas said in interviews. The Trump-era anti-immigrant rhetoric of being tough on the border and building the wall has not repelled these voters from the Republican Party or struck them as anti-Hispanic bigotry. Instead, it has drawn them in.“Our parents came in a certain way — they came in and worked, they became citizens and didn’t ask for anything,” said Ramiro Gonzalez Jr., a 48-year-old rancher from Raymondville, on the northern edge of the Rio Grande Valley. “We were raised hard-core Democrats, but today Democrats want to give everything away.”Ramiro Gonzalez Jr., a rancher in Raymondville, is among Latino conservatives who are reshaping South Texas politics.Jason Garza for The New York TimesFor years, the Republican primary in the Rio Grande Valley was an afterthought, a sleepy election overshadowed by a Democratic primary that grabbed all the attention and candidates. But this year, in the run-up to the Texas primary election on Tuesday, there has been a flurry of Republican rallies, door-knocking and events, including at the Hispanic community center that the Republican National Committee opened in McAllen four months ago.The Republican gains run far deeper than Mr. Trump and, in some ways, predate him, interviews with Hispanic voters and candidates showed. Republican candidates are building on a decades-long history of economic, religious and cultural sentiment that has veered toward conservatives. George W. Bush performed even better in his 2004 re-election campaign in the region than Mr. Trump did in 2020. Many of those who voted for Hillary Clinton or Barack Obama for president and then flipped for Mr. Trump had previously backed Mr. Bush.For the moment, Republicans in the Rio Grande Valley remain a minority. Last year, a Republican was elected mayor of McAllen, the Valley’s second-most populous city, and a Democratic state lawmaker in Rio Grande City switched to the Republican Party, both of whom earned praise from the Republican governor of Texas, Greg Abbott. But Democrats still dominate the vast majority of local elected offices in the Valley.A sign outside the Republican National Committee’s Hispanic community center in McAllen.Jason Garza for The New York Times“It’s still relatively insignificant, when you look at Democrat versus Republican overall,” said Representative Vicente Gonzalez, a South Texas Democrat who narrowly won his 2020 re-election. He is now running in a redrawn neighboring district and is likely to face Ms. Flores as his Republican opponent in November. Though he said he was confident voters would “come home” to Democrats this fall, Mr. Gonzalez criticized the party for not doing more to focus on the region.A Guide to the Texas PrimaryThe 2022 midterm elections begin with the state’s primary on March 1.Governor’s Race: Gov. Greg Abbott’s rightward shift will face a test in November. His likely challenger, Beto O’Rourke, is haunted by his 2020 presidential bid.Attorney General’s Race: Whether Ken Paxton can survive the G.O.P. primary may be the biggest test yet of Donald Trump’s continued power over voters.A Changing Landscape: Issues like abortion and immigration are driving Hispanic voters in Democratic strongholds to switch parties and prompting liberal candidates to shift tactics.A Deepening Divide: Competitive districts are being systemically erased across the country. Texas is an especially extreme example.New Voting Law: Officials have rejected thousands of absentee ballots based on new requirements, an alarming jump ahead of the primary.“So far I see no action,” Mr. Gonzalez said. “I’ve had to rely on myself, not on the national party coming down here to save us, so in that respect, it’s sad.”For decades, conventional wisdom held that the more Hispanic voters showed up to the polls, the more precarious the political future would be for Republicans. But the inverse has lately been reshaping South Texas politics: As tens of thousands of new voters have gone to the polls, Republicans have gained more than Democrats. In Hidalgo County, which includes McAllen, Mr. Trump received nearly twice as many votes in 2020 as he did four years earlier.Mr. Trump’s performance in these border counties was one of the big surprises of 2020, rattling Democrats who had assumed that Trump’s anti-immigrant rhetoric would alienate Latinos. In this year’s midterm elections, South Texas is the setting for the only competitive House race in the state, and both parties now consider Hispanic voters across the country a potentially decisive swing vote.At a dinner for Ms. Flores’ campaign at Don Chucho Tacos y Tequilas in the border city of Brownsville, her supporters began with a prayer and the pledge of allegiance to the Texas flag. They wore wide-brimmed cowboy hats and red MAGA caps. They applauded when the mariachis took the stage — and when Ms. Flores introduced her husband, an off-duty Border Patrol agent.“We’ve been voting California values, Austin values, but not South Texas values,” Ms. Flores told the crowd. She added, speaking the Spanglish so prevalent in the region, “Spread the chisme. Somos Americanos.” Spread the word. We are Americans.“This,” she continued, “is our country.”“I want to bring God back into politics,” said Luis Cabrera, the pastor of City Church in Harlingen, Texas.Jason Garza for The New York Times‘We feel under attack’Pastor Luis Cabrera, 44, remembers the fear in his parents’ eyes when they fled Nicaragua in 1979, in the midst of the Sandinista revolution.His father, a lawyer for the ousted president, received death threats and after obtaining visas from the American embassy there, the family left nearly all they had behind, flying with $10,000 in cash on a flight to Washington, D.C. Eventually, Mr. Cabrera’s father found work as an immigration paralegal in Houston, and then took the family to the Rio Grande Valley.Now, Mr. Cabrera runs City Church, a small congregation in a former warehouse in the border city of Harlingen. He estimates that his church is 96 percent Hispanic, and 100 percent Republican.“The people coming now seem to be less willing to work and are more dangerous compared to how it used to be,” Mr. Cabrera said. “I’m not saying all of them, but trust me, there’s a lot of people who are crossing this border and they don’t care about this country. They want to just commit crime. They want to just come make money the wrong way. They don’t want the American dream.”The Rio Grande Valley lies at the southeast corner of the U.S.-Mexico border, an amalgam of dozens of small cities and towns across four counties, a mix of recently developed strip malls and centuries-old ranch land. The Stars and Stripes and other flags fly from the back of large pickup trucks and flagpoles installed on front yards. The vast majority of the Valley’s nearly 1.4 million residents speak Spanish and have ties to Mexico. Pockets of deep poverty remain, and residents have long viewed Border Patrol and other law enforcement jobs as a reliable path to the middle class. For all the talk by Republicans of border chaos and of dangerous migrants, crime in McAllen is at a historic low.Mr. Cabrera sells T-shirts at the entrance of his church.Jason Garza for The New York TimesThe gulf between the undocumented Central American migrants crossing the border and the Latino residents of the Valley is deep and wide.Many residents are Mexican Americans who have lived in the region for four or five generations, or proudly proclaim their parents and grandparents came to the United States legally. They know both Border Patrol agents and undocumented Mexican immigrants who have lived and worked in border cities for years. Those who are Republicans say they do not see their views on immigration as hypocritical or anti-Hispanic. Instead, they see themselves as a bulwark for law and order. A few thousand Border Patrol agents live and work in the region, many of them Hispanic, adding to a pro-law enforcement ethos that shows up in churches, schools and local politics.“We’re in a war — a war of ideas,” said Jessica Martinez, 33, a Brownsville stay-at-home mother who said she had never voted until she cast a ballot for Mr. Trump in 2020, after she grew frustrated with the relentless outrage against him from liberals. “That’s how we as Christians see it. We feel under attack.”In Harlingen, Mr. Cabrera turned the entrance of the church into a retail space. He displays and sells T-shirts reading Make America Godly Again and Make America Repent. For years, he said, he avoided speaking about politics from the pulpit. But in the last year he has hosted several Republican leaders at the church, including Mr. Abbott.“I want to bring God back into politics,” Mr. Cabrera said. “And so that’s what I’m doing.”‘I worry about our values’Joe Cadriel, a 57-year-old veteran of the gulf war’s Desert Storm and a retired social worker, has rarely placed campaign advertisements on his front lawn. But he made an exception for Ms. Flores, the Brownsville Republican running for Congress.Mr. Cadriel and his wife, Diana, a retired educator, both voted for Hillary Clinton in 2016, and then cast their ballots for Mr. Trump four years later, convinced that he would best protect the southern border, a mere 10 miles from their Weslaco home.The couple grew up in the Rio Grande Valley as children of conservative Democrats, and they harbored a proud independent streak. Mr. Cadriel has been infuriated by illegal immigration for as long as he can remember — he said he once left a job because he felt too angry seeing food stamps and other benefits going to children of unauthorized immigrants.“I’m OK with people coming in saying I’m going to do something productive,” Mr. Cadriel said. “But that wasn’t what was happening. You’d have these people claiming they needed food stamps for their children, but their children were babies, so who do you think was benefiting from it? They were just trying to take advantage.”Joe and Diana Cadriel of Weslaco, Texas, voted for Hillary Clinton in 2016 and Donald Trump in 2020.Jason Garza for The New York TimesThe Cadriels equate walking away from the Democratic Party with getting an education, not from college courses or books, but from conservative media and scripture. A retired educator and churchgoing Catholic, Ms. Cadriel, 57, slowly began to feel that her family’s traditional values were under attack. She stopped watching Good Morning America and The View in favor of Fox News.“I worry about where we’re headed, about what will and won’t be allowed,” she said. “I worry about our values.”Republican candidates like Ms. Flores hope to capitalize on the Cadriels and other former Democrats.Ms. Flores’ parents worked as migrant farmworkers, moving each year to pick cotton in West Texas. Though her parents were Democrats, Ms. Flores said she was raised with “conservative values” and was drawn to Republicans because of her anti-abortion views. Soon after graduating from South Texas College in 2019, she became involved with the Hidalgo County Republican Party, volunteering as the Hispanic outreach chair while she worked as a respiratory therapist.Ms. Flores’ campaign signs do not mention policy or party, but instead highlight three words: “Dios, familia, patria.” God, family, country. More