Julian Castro in his office at the Department of Housing and Urban Development, in a portrait taken in 2014. (Sarah L. Voisin/The Washington Post)

Julián Castro cut into his overcooked brisket, dumped four artificial sweeteners into his iced tea and shifted in his seat. It’s not that he didn’t want to answer the question, it’s just that he couldn’t.

Sure, he’s thought about the possibility of being picked as Hillary Clinton’s running mate on the Democratic ticket. How could he not? What with the “Ready for Julián?” and “Castro Is in VP Training Camp” headlines percolating out of the political press. Even Stephen Colbert tried to trick the 41-year-old secretary of housing and urban development into saying he wanted to be vice president in a recent late-night appearance.

And it’s not that he’s ashamed of his ambition. You don’t run for mayor of San Antonio at 30 or become the youngest member of President Obama’s Cabinet without having a healthy ego. But running for vice president, if it’s even possible for someone to run, is different. If Castro dares show too much interest, he looks desperate and his chances evaporate. Looking uninterested, however, is also not an option.

“What makes this different is that this position isn’t really yours to talk about,” Castro finally said, slipping into second-person. “It’s not my decision; it’s nobody’s to claim.”

Housing and Urban Development Secretary Julián Castro spoke with The Post's Manuel Roig-Franzia about the 2016 presidential campaign and his name in the airwaves as a possible vice presidential candidate. (Meena Ganesan/Washington Post Live)

There is perhaps no better and no worse time to be Julián Castro. He’s an exciting, fast-rising Latino politician, coming of age politically just as the Democrats need him most. He will certainly at least make Clinton’s short­list as a running mate. But what if she doesn’t pick him? What if she’s not even the nominee? He comes from Texas, a conservative-leaning state that is years away from electing a Democrat statewide. Maybe there’s another Cabinet position for him in the future, but the Cabinet was never his real goal. He could always retreat into the private sector, but that could squelch the momentum of a young man with ambitions still burning.

“This time I don’t know what I would do next,” he said. So why does Castro, on the cusp of going boom or going bust, seem so calm? It helps to know how the game is played. And it helps to have failed before.

O brother, where art thou?

Long before Castro was in the mix to become the second-most powerful person in America, he was a punch line, embarrassed by a Texas riverboat parade.

It was April 2005, the day of an annual floating extravaganza along the San Antonio River, and Castro’s big commitment for the evening was to ride a barge with his fellow city councilmen.

And there he stood — or so it seemed — waving to a quarter-million cheering constituents from the front of the boat, a leading mayoral candidate with a big grin and an even bigger future. The only problem. . .

“I remember watching the parade from home and saying to my wife, ‘That’s not Julián, that’s his twin brother Joaquin,’ ” said Christian Archer, who at the time ran the mayoral campaign of Julián’s opponent. Sure enough, moments later Archer’s communication director called: He was at a town hall across town, and Julián was there, too.

Archer’s candidate, Phil Hardberger, a 71-year-old former judge, had been trying to paint the 30-year-old Castro as too young and callow to lead the city. These kind of “Parent Trap” shenanigans could help make his case.

“If you’re 18 years old and having a date, it might be a youthful prank when you swap out your brother,” Hardberger told reporters shortly after word got out about the incident that would be dubbed Twinsgate. “But when you’re running for mayor of a city with 1.3 million people and sending in your brother as an impersonator, I do see a problem with it.”

Julian Castro, center, with his brother, Rep. Joaquin Castro, left, at the 2015 State of the Union address. (Mandel Ngan/AFP)

Julian, left, and Joaquin Castro on stage at the 2012 Democratic National Convention, when Julian’s keynote launched the brothers into a national spotlight. (Daniel Acker/Bloomberg)

The Castros called it a misunderstanding, that Julián had invited his brother, then a state lawmaker, as his guest and ended up getting stuck at another event. They tried to turn it into a joke, toting shirts that said “I’m Julián” and “I’m Not Julián” to national television shows. But not everyone laughed.

“Isn’t that some kind of deception?” a straight-faced Harry Smith asked the brothers on CBS’s “Early Show.” “Julián, do you feel like you owe the people of San Antonio an apology?”

“It helped complete the narrative,” Archer recalled. “We wanted people to think of him as too young, and in the end, the guy with the gray hair won out.” Julián lost the mayoral race by a hair to Hardberger.

It was, and remains, Castro’s one setback in a meteoric career. Four years later, he was elected mayor, and two years after that was tapped to deliver the keynote address at the Democratic National Convention. In 2014, Obama picked him to replace Shaun Donovan at HUD. But Castro still thinks back to that losing campaign.

“That was a turning point,” Castro said. “When you lose in that way, very publicly, it’s personal. It was also a reminder that you can’t count on the future playing out the way you want.”

Joaquin, now a second-term U.S. congressman representing a chunk of San Antonio, agreed. “We learned a real lesson about nuance,” he said over lunch at the members’ dining room in the Capitol. “In the media and in politics, there isn’t much nuance. There’s no fighting against a narrative of twins switching places, it’s too compelling a story to be read any other way.”

Nuance is key for the Castro brothers. It comes with the territory, both of them having lived with near-facsimiles since birth. They have the same bushy eyebrows on expansive, wrinkle-free foreheads, the same left-side part in their jet-black hair, the same flecks of gray around the temples. Close observers might notice that Julián has the thinner cheeks, and slicker suits, and those who know them best say you can tell them apart by their eyes.

Sons of a single mother — Rosie Castro, a prominent liberal activist in San Antonio — they attended Stanford together, then Harvard Law, and even practiced law together for a while. Joaquin is the more gregarious one, better equipped to be thrown into a manic House of 435 people. Julián was always more self-contained, the man equipped for an executive role.

Neither is fluent in Spanish, a point that has dogged them since becoming national figures. At lunch Joaquin makes a point of conversing with one of the cafeteria workers.

“People think that you either are fluent in Spanish or can’t speak it at all,” he said. “Not everything is that black or white.”

But for every narrative that’s “too good to check” working against them, there are at least as many in their favor. Take the time the twins both ran for Stanford’s student senate and received exactly 811 votes each, becoming a sensation on campus.

“I’m pretty sure it was a computer glitch,” Joaquin said with an impish smile. “But it was a good story.”

How to (not) run for VP

Archer felt guilty. He was glad his candidate had won the 2005 mayoral race, but he felt like the Twinsgate narrative was a low blow. So when he bumped into Julián and Joaquin at a Mexican restaurant shortly after the election he tried to avoid eye contact.

“Julián chased me down and asked me to have lunch with them,” Archer said. “I figured it would be uncomfortable, but they didn’t want to hit me about the negative ads. They were just incredibly inquisitive, incredibly impressive. By the end of it, I told them I’d never be on the other side of them again.” He went on to run campaigns for both Julián and Joaquin.

As mayor, Castro’s biggest initiative was leading a voter referendum to expand pre-kindergarten education. But his rising-star profile outshone his accomplishments, especially after his convention keynote.

He turned down his first offer to join the administration, as secretary of transportation. But when it became increasingly clear that statewide positions were unattainable for Democrats in Texas, he jumped at the chance to run HUD.

Henry Cisneros, who like Castro was once HUD secretary and mayor of San Antonio, urged Castro to take the position.

“He wouldn’t be getting this kind of consideration if he was still just the mayor,” he said.

Julian Castro introduces Hillary Clinton at a October 2015 campaign event in San Antonio. (Eric Gay/AP)

Castro knows the party could use some youth and diversity, especially if Republicans nominate Sen. Ted Cruz or Sen. Marco Rubio; confidants say he won’t be surprised to be one of the finalists if Clinton gets the Democratic nomination. She has even hinted as much onstage at a Latino business conference in San Antonio. And so Castro admits his job as secretary of HUD — a job that has him crisscrossing the country, getting to know politicians in many states, sitting down with the New York Times editorial board — has been good practice for whatever comes next.

“One of the more intriguing parts of this role [at HUD] is that you can’t just say anything you want,” Castro said. “It doesn’t just reflect on you, it reflects on the administration, and in a sense it’s a good precursor to this other stuff.”

But what comes next is out of his hands, and getting tapped as a VP nominee is no sure thing. He’s still young and relatively inexperienced. He’s fairly moderate — hardly the guy to rally the Bernie acolytes. If Clinton decides she wants a traditional running mate with decades of Democratic battle scars, from a state that matters in the general, and who does speak fluent Spanish, she might choose Sen. Tim Kaine from Virginia.

So what can Castro do? He has been hitting the road for Clinton, stumping for her in Nevada and Iowa. He can keep plugging away at HUD projects like bringing Internet to public housing. But getting to be VP is so often about style over substance. So mostly he can wait — a challenge for someone who has been climbing the ladder since college.

I asked Joaquin what people would think of his brother if he started saying that he wanted the job.

“They’d say, what an a--hole,” he laughed. “What an arrogant a--hole.”

So instead, Julián says this: “I don’t deny that I’m ambitious: Anybody in politics who says there’s no ego involved in running for office is bulls----ing you. But at the same time, that doesn’t mean that there’s a grand plan for my future.”

This is what he and his brother learned from their Twinsgate years: that nothing is certain in politics, but that a loss won’t necessarily derail your career. And that it’s their job to adapt.

“I’ll tell you,” Joaquin said, “if Julián does become vice president, I’m either going to shave my head or grow a beard, just to make sure no one mistakes me for him.”