What Julian Castro can do for Obama

Editor's note: Ruben Navarrette Jr. is a CNN contributor and a nationally syndicated columnist with the Washington Post Writers Group. Follow him on Twitter: @rubennavarrette

Charlotte, North Carolina (CNN) -- Julian Castro is ready for his close-up. The Mayor of San Antonio is already a hot commodity in his home state of Texas and throughout the Southwest.

Tonight, when the 37-year-old steps up to the lectern and becomes the first Latino to deliver a keynote speech at the Democratic Convention, the rest of the country will get a chance to see what all the fuss is about.

There's a lot to see. I've known Julian for eight years, and I've interviewed him a dozen times. He's one-half of a dynamic duo; his twin brother, Joaquin, a Texas state representative who is a shoo-in to win a new congressional seat in November, will introduce him tonight. Both are graduates of Stanford University and Harvard Law School.

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With the news that one brother would introduce another, what was already going to be a big story for the Latino community in America -- 50.5 million strong, 16 percent of the U.S. population on its way to 25 percent a few decades -- just became a huge story. The optics will be out of this world.

According to the polls, Obama is still ahead of Romney by more than 30 points with Latino voters. But Obama's Latino support has taken a hit because of his heavy-handed immigration enforcement record. Now, thanks to the Castros, don't be surprised if that support jumps 5 points overnight.

The twins' message will be something like this: Thanks to the hard work and sacrifice of our family, we have lived the American Dream. We love our community and our country, and -- if you support this president and this party -- more of these types of stories will be written.

Mitt Romney's Latino outreach efforts are about to take a direct hit.

I spent the morning of the speech shadowing my friend from one media interview to another, and squeezing in a few questions of my own whenever I could:

-- About what it's like to live a moment like this:

"The enormity of it is really impressive," Castro told me. "This is one of those moments where you know you need to be enjoying it as it's happening, but that's also hard to do because it's moving so fast."

-- About what he hopes his 3½-year-old daughter Carina, who accompanied her father to Charlotte and knows only that "Daddy is giving a big speech," takes away from tonight when she reads press clippings years from now:

"What I hope is that one day when she watches it that she understands that her family came here and sacrificed and worked hard to achieve the American Dream," he said. "And that this was the moment, the pinnacle of it. And I hope that she's very proud. And I also hope, like any dad, that she goes further than I did."

Live blog: Democratic National Convention

-- About what he hopes his speech will mean to his mother, Rosie, who a generation ago was active in the Raza Unida Party (a third party born in the 1970s out of frustration with both Democrats and Republicans:

"I hope that my mother takes away that all her generation did, the sacrifices she made, the activism that she engaged in with folks of her generation, led us to this moment," Castro said. "This is the wonderful progress that the country has achieved not just for them but for so many Americans, that America has lived up to its highest ideals and our family is one example of that."

-- Lastly, about the reaction he's getting from the large contingent of Spanish-language media that is covering the convention, whose audience is more Mexican than Mexican-American, more immigrant than native-born:

"The interviews are always very warm," he said. "You can hear in people's voices a certain pride and aspiration, and of course that feels very good to me. I just want to make sure that I do a great job, and that I don't let people down."

There is little chance of that. The Castros don't let people down; they lift people up.

Get ready, America. A new generation offers a leader. And a population of people who helped build this remarkable country, and who have repeatedly answered the call to defend it, have finally come into their own.

We Mexican-Americans are known for our humility. But is there pride in that? You had better believe it.

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The opinions expressed in this commentary are solely those of Ruben Navarrette Jr.