By Kate Linthicum, Los Angeles Times (TNS)

OTTUMWA, Iowa — Julian Castro, a rising star in the Democratic Party, was stumping for Hillary Clinton in southeastern Iowa on Sunday when a union leader extended a hand and a question in Spanish.

“I heard Clinton might pick you for vice president,” said Jose Pulido, who represents workers at a hog slaughterhouse that has helped draw thousands of Latinos to this small city straddling the icy Des Moines River.

Castro flashed a toothy smile. “Quien sabes,” he answered, shaking his head. Who knows?

As the secretary of Housing and Urban Development and former mayor of San Antonio, Castro’s ethnic roots, up-from-the-bootstraps story and quick ascent in politics have earned him comparisons to President Barack Obama. He is frequently mentioned as a possible vice presidential pick for Clinton, should she prevail as her party’s nominee.

In something of a test of Castro’s campaigning abilities, he barnstormed Iowa in the final days leading up to the state’s Feb. 1 caucus. He visited several small cities with growing Latino populations and warned voters about the dire consequences of a Clinton loss and the possible return of the White House to Republican control.

“We absolutely can’t afford to hand over the presidency to the Republican Party,” Castro told a crowd in Fairfield, his second stop of the day. “Can you imagine what would happen if you have Speaker (Paul) Ryan, Senate Majority Leader (Mitch) McConnell and President Trump?”

“We’ve seen what they’ve done when they’ve had that kind of power,” he added, hinting at the kind of attack-dog sensibility that presidential candidates often rely on in a running mate.

In recent months, several leading Latino leaders, including former Housing Secretary Henry Cisneros, have called on Clinton to add Castro to her hypothetical ticket. The national Hispanic Chamber of Commerce issued a formal endorsement of Castro for vice president Saturday, even though it hasn’t yet endorsed a candidate for president.

Pollsters and pundits agree that any presidential ticket could benefit from a qualified Latino to help win votes from the nation’s fastest-growing demographic. And at 41, Castro would provide a generational contrast to 68-year-old Clinton.

Here in Iowa, a rapidly expanding Latino electorate mirrors the United States as a whole, where a record 27.3 million Latinos will be eligible to vote this year. The state’s Latino population grew 110 percent between 2000 and 2014, and Latinos constitute 10 percent or more of eligible voters in 11 of the 99 counties here.

The rise of Latinos in U.S. society is also reflected in Castro’s story, which he repeated often in Iowa.

Castro and his identical twin brother, Joaquin, were raised in San Antonio by their Chicana activist mother and Mexican immigrant grandmother. They graduated together from Stanford University and Harvard Law School before launching parallel political careers.

Joaquin was elected to the Texas Legislature and is now a Democratic member of Congress representing part of San Antonio.

Julian, who was born one minute earlier and jokes that he is older — and wiser — than his brother, was elected at age 26 to the San Antonio City Council, becoming its youngest-ever member. He went on to win three terms as mayor, where a key initiative was the passage of a sales tax increase to help pay for an expansion of prekindergarten, part of a wave of similar proposals among Democrats around the country in recent years.

In 2014, Obama offered Castro a position in his Cabinet. Castro’s short tenure as Housing secretary will end when Obama leaves office in a year.

Castro says he decided to endorse Clinton in part because she “has the deepest ties and the longest track record of working for the Latino community,” citing her work registering Latino voters in south Texas in the 1970s.

Clinton has said she would “look hard” at Castro for any position in her campaign or administration. Other names floated as possible Clinton vice presidential picks include Virginia Sen. Tim Kaine and New Jersey Sen. Cory Booker. Both campaigned in Iowa for Clinton over the weekend as well.

For his part, Castro has become practiced at ducking questions about the vice presidency, saying he is focused on winning her the nomination.

And a lot of work lies ahead. While Clinton won a coveted endorsement from the Des Moines Register on Saturday, polls show Sen. Bernie Sanders slightly ahead in what is shaping up as a closely fought battle in this state.

©2016 Los Angeles Times. Distributed by Tribune Content Agency, LLC.

Photo: Democratic U.S. presidential candidate Hillary Clinton waves with U.S. Secretary of Housing and Urban Development Julian Castro at her side during a “Latinos for Hillary” rally in San Antonio, Texas October 15, 2015. Castro endorsed Clinton’s campaign for president.   REUTERS/Darren Abate