SAN ANTONIO, United States (AFP) — Julian Castro, the telegenic former mayor of San Antonio, Texas and an Obama-era cabinet member, launched his bid Saturday to become the nation’s first Hispanic president, emphasising a message of hope and diversity at a time when Americans are locked in angry debate over immigration and border security.

“I am a candidate for president of the United States,” the 44-year-old Castro told a large crowd in San Antonio’s historic Guadalupe Plaza, in a speech that frequently invoked the immigrant heritage that brought his family to the US from Mexico.

Often called a rising star in the Democratic Party, Castro, who was Obama’s secretary of housing — and the youngest member of that cabinet — is expected to be part of a huge and diverse field of candidates eager to challenge President Donald Trump.

At a time when the federal government has been partly shut down as Trump demands funds to build a wall on the Mexican border, Castro sounded a contrasting message.

He said San Antonio, a city that is nearly two-thirds Hispanic, “represents America’s future: diverse, fast-growing, optimistic.”

“Yes, we must have border security, but there is a smart and humane way to do it. And there is no way in hell that caging children is keeping us safe.”

“We say no to building a wall and say yes to building community,” he said, to roars from the crowd.

Urging his supporters to look around the blue-collar neighbourhood where he grew up, Castro said, “There are no front-runners that are born here, but … with big dreams and hard work, anything is possible in this country.”

He added that his grandmother Victoria would surely have been amazed when she arrived from Mexico in 1922 — she went on to work as a maid and a cook— had she known that one grandchild would end up in Congress and the other as a presidential candidate.

Castro’s twin brother Joaquin, who introduced him Saturday, is a member of Congress. The two rode to the event together on the same bus line that once took them to public school.

Julian Castro’s strong oratorical skills, experience in the Obama cabinet and as mayor of the nation’s seventh largest city, not to mention his telegenic charisma, could help propel him into the top tier of Democratic candidates.

Castro’s national profile rose sharply in 2012 when he became the first Latino to deliver a keynote speech at the Democratic national nominating convention.

A Latino candidate would be expected to generate enthusiasm among the country’s large and growing population of Hispanic voters. About two-thirds of them supported Hillary Clinton in 2016.

But he would start out as one of the underdogs in a political showdown that may well feature heavyweights like former vice president Joe Biden, US senators Elizabeth Warren, Bernie Sanders and Kamala Harris, and perhaps even billionaire businessman Michael Bloomberg.