Julián Castro, the mayor of San Antonio in Texas, is walking with me from his office to Acenar, a favourite Tex-Mex restaurant a few blocks away in the heart of the city’s old Spanish mission. Every few ­seconds a motorist or passer-by waves good-naturedly to him. He’s easy to spot: Castro, 36, cuts a striking figure, his matinee-idol good looks enhanced by a sharp suit, shiny dark shoes and an all-too-easy charm. He seems to be smiling all the time.

He has good reason to be happy. Castro, who was elected in May 2009, tells me that the mayor’s role is more like being chairman of the board of the city council than its chief executive. But big city mayors in the US have a high profile. Over the past 10 years San Antonio has grown to be the seventh-largest city in the US. About two-thirds of its 1.3m population is Hispanic, making Castro’s position the perfect springboard for a coming star of the Democratic party.

“Hey!” A man with matted beard and ragged clothes loitering on the pavement yells to catch Castro’s attention as we stride past. “Ah,” he says, eyeing the mayor’s left hand as though he has just solved a puzzle. “You got the ring.” He gives us a knowing look and then insists he needs an appointment with mayor “Julián”. (Castro pronounces his name the Spanish way – Hoo-Lee-An.) The mayor flashes a smile and walks on, waving over his shoulder and telling the man to get in touch with his office to set up a time.

The mayor’s wedding ring (he and his wife Erica have a two-year-old daughter) is a tell-tale sign. It is what distinguishes him from his identical twin brother, Joaquín, who is unmarried but on a parallel political career track. Joaquín is a member of the Texas state house and is seeking a seat in Congress in next year’s elections.

The Castro brothers are symbols of the rise of Hispanics in national politics. While the US has grappled with racial politics throughout its history, the vast Hispanic community is the latest battleground as the major parties seek an edge over their opponents in a deeply divided electorate.

Hispanics are by far the fastest-growing group in the US, responsible for more than half of the national population gain of 27.3m people in the decade to 2010 – and nearly 90 per cent of the growth in Texas. Hispanics will soon be the largest community in California and Texas, the two most populous states in the country.

Hispanic voters favour Democrats by a margin of about 60 to 40 per cent. This voting pattern could, in the 2012 elections, keep Barack Obama in office for a second term and could propel Castro, or someone like him, into the White House in future.

Julián and Joaquín Castro were born in San Antonio in September 1974. Their mother, Rosie Castro, was then a well-known Chicana (Mexican-American) activist, one of the leaders of a group known as La Raza Unida, agitating for Hispanic rights and identity. She raised her sons largely as a single mother.

This life story might give rise to comparisons with Obama, who came to embody the political aspirations of his community and race. And, like Obama, the Castro brothers have Ivy League degrees, graduating together from Stanford (where Julián majored in communications and political science) and then Harvard Law School. Julián was so keen to get into local politics in San Antonio that he launched his campaign from his Harvard dorm so he could run for the city council straight after graduation, winning his seat in 2001. His brother entered the Texas state house in 2002.

Yet the Castros might be better compared to David and Ed Miliband, without, so far, the psycho-drama that the British brothers generated when they ran against each other to lead the Labour party in 2010. The Milibands, sons of a Marxist academic, have moved towards the political centre in their careers, just as the Castros have after their upbringing in grassroots politics.

As we arrive at the restaurant, Castro arches his eyebrows when I ask whether he has endorsed his brother in the forthcoming Democratic primary for the seat in Congress. “Of course,” he says. He describes his brother as his best friend. Castro’s arrival doesn’t turn heads among the staff. He comes here regularly and they are clearly used to his presence, leading us to a table in the centre of the restaurant without fanfare.

Acenar bills itself as “HotMex, CoolBar”. It sits astride the San Antonio River Walk, an old flood channel transformed into an attractive network of waterways lined with restaurants and attractions – “the second-biggest tourist attraction in Texas,” the mayor tells me with civic aplomb. The biggest tourist attraction in Texas is just five minutes further down the road. The site of the Alamo siege of 1836 is, for most visitors, a symbol of liberty, the place where a heroic band of fighters held out against an overwhelming force of Mexican troops for 13 days in a pivotal battle of the Texan revolution. For Mexicans, and some Mexican-Americans, however, it is a symbol of humiliation and defeat.

The restaurant’s decor is shiny and new and the menu performs similar tricks, repackaging hardy Mexican fare with a touch of modernity. We are both in a no-frills mood, and order enchiladas de mole, chicken-filled tortillas with beans and rice on the side. Castro has iced tea, and I have a Pepsi, along with our glasses of iced water – always served automatically in American restaurants.

The iced water reminds him of his only trip to London, on holiday in December 2007. He says it was the “little things” that got to him there. “Of course, driving on the wrong side of the road but also no ice – people don’t have ice in their drinks.” I suggest the climatic difference between sun-baked San Antonio and grey London might explain that cultural quirk.

Castro has been tipped for success to the point where some in his home state are already sick of hearing about it. The Texas Tribune, an online magazine, noted in 2010 that his “future electoral prospects are a frequent-bordering-on-yawn-worthy topic of conversation.”

Castro is not the first Hispanic politician from San Antonio to be marked for great things. Henry Cisneros rose from mayor of the city to become a cabinet member in the Clinton administration before his career ended in the late 1990s after a sex scandal. Nevertheless, I wonder if Castro’s carrying of the expectations of his community is a great burden.

“Part of the blessing of being young is feeling that a lot less than one might think,” he says. “It is very flattering and I would be lying [if I said] that I never think about that. But there are certain challenges in politics that sober you up.”

The first is that Texas is a “very red [Republican] state”. Democrats have not won an election for any of the state’s 29 elected offices since 1994. Castro says he aims to serve four two-year terms as mayor, which would take him to 2017.

That would set him up for a run at one of the most coveted positions in the country – Texas governor, a post currently held by Republican presidential hopeful Rick Perry and before him, George W Bush. It would be unthinkable for a Democrat to win that office now, let alone covet it as a step in an even loftier career path leading to Washington. But, by 2017, does he think the growth in the number of Hispanic voters may mean that even Texas could turn “blue”, or Democratic? “I think maybe by then it could be a purple state,” he smiles. “Not blue but a state that could elect either one.”

One problem for a politician relying on the Hispanic vote is that their turnout is low on election days. Hispanics made up more than 16 per cent of the US population in 2010 (according to the Pew Research Center) but only 10 per cent of eligible voters, because of their relative youth and the fact that so many are in the US illegally. They make up only 7 per cent of actual voters. Although the community is now well-settled and made up largely of second- and third-generation migrants, it still lags in wealth and education.

About 40 per cent of Hispanics in Texas don’t graduate from high school. That already means, Castro says, that by 2040, “the number of people with high school and bachelor degrees will be less than [it is] now, because of the growth of an under-educated community”.

Castro struggles to explain why this is the case. “There is tremendous love for family and children and aspiration to succeed but less of the know-how to shepherd kids through the education system,” he says. “Sometimes, there is a feeling that teachers know best and a shying away from parental involvement.”

Our food arrives. The waiter warns us to take care with the hot plates. I somehow don’t process this instruction and nearly scald myself picking mine up. “They mean it when they say hot,” Castro says dryly.

The low Hispanic turnout is something that Castro reckons will change, if only because of the focus on the importance of their vote. As with African-Americans, he claims that conservatives intentionally create barriers for Hispanic voters at the ballot box, such as rules demanding IDs.

Yet Hispanic communities are social conservatives and highly religious. George W Bush famously courted them when he was Texas governor in the 1990s. “That seems like aeons ago now,” says Castro. “The entire party has moved so far to the right.” He recalls participating in a debate on immigration this year in New York when he says his opponents talked about Hispanic immigration “as somehow lesser than previous waves of immigration”. The proposition for debate – “Don’t give us your tired, your poor, your huddled masses” – underlined the sentiment that Hispanic immigration was not good for the US.

“It is not stated in such blunt terms but basically they were saying folks were inferior,” he says. “That argument is not commonly made out in the open but this is mainstream Republican talk and the Hispanic community picks up on that. Of course it is going to colour how they view conservatives,” he adds with conviction. “And it has and I believe that it should.”

He admits he is conscious not to sound angry. Obama has exercised a similar discipline. It seems to be a rule of American politics that an angry black or Hispanic man does not play well with the broader electorate.

Castro’s mother was different in her youth. “She was very active and, in keeping with the times, very vocal about the needs of the Hispanic community,” he says. “But these are different times. This generation sees things though a different lens. America has made a tremendous amount of progress in the last 40 years.”

He says his mother, who is now 64 and works in a local community college, recognises America’s ability to improve. “She is at peace with the progress that has been made and is enjoying seeing it. She is not the fiery 23-year-old that she was.”

But, I ask, is it true that, like many Mexican-Americans, she still doesn’t like the Alamo?

“I am sure she still doesn’t,” he smiles. “She grew up with a quite different experience from what my brother and I had. That has obviously impacted her world view about things like the Alamo. We got to grow up in a time when we were less burdened with that.”

So you didn’t grow up feeling angry and disenfranchised? “No.”

Castro sounds firm, not angry, when he talks about the distant budget battles in Washington and Republican demands for cuts to health spending and pensions.

The debate, he says, is coming to a crescendo. “I don’t believe that America is at the point where people are unwilling to foot the bill for Medicare and social security, yet that is the ideology that is being rammed down people’s throats.”

As lunch winds up, he talks once more about his current job, and beats San Antonio’s drum as a successful Hispanic city that has sailed through the downturn far better than the rest of the country. Like the rest of Texas, San Antonio did not suffer a housing crash and has benefited from high oil prices. “This is not what people think; [they think] that if you had a large Hispanic community, it would be a poor town and that is not the case.”

With that he grabs the bill and insists on paying. Given that the FT has very strict rules which mean the guest should never pay for lunch, I object strongly. To no avail. The deed is done. It is the only impolitic thing he has done all day.

Richard McGregor is the FT’s Washington bureau chief

Hal Weitzman is the FT’s Chicago correspondent

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