Story highlights San Antonio Mayor Castro slated to head Housing and Urban Development department

Ruben Navarrette says the move could better position him to be 2016 running mate

He says Democrats could gain, and GOP could lose, points with Latino voters this year

Navarrette: HUD secretary could turn out to be a dead-end job

Normally, when an elected official has to make difficult choices, balancing ambition with practical concerns, it boils down to a personal decision. But when the official is a political rock star who might just be the first member of his community to become president, the whole decision-making process plays out in public.

Take the case of Julian Castro, the San Antonio mayor who has now thrown political observers a curveball by accepting an offer from President Obama to join the Cabinet as secretary of housing and urban development.

Castro has been talked about before as a potential 2016 candidate for vice president. The idea of his moving to Washington, if he's confirmed at HUD, is sure to keep tongues wagging for the next couple years. It will also provide plenty of opportunity for unsolicited advice. It seems many people have an opinion on whether Castro has made a shrewd career move or derailed an otherwise promising political future.

I've known Castro for about 12 years, and he's a friend. I want what's best for him. I'm just not sure this is it.

Ruben Navarrette

Why should others care about this choice? Well, for starters, because you can't begin to understand America in the 21st century without an appreciation for the footprint being left by 52 million Hispanics -- a demographic estimated to account for 25% of the U.S. population by 2040. Two-thirds of that population is Mexican or Mexican-American, and Castro is the most prominent politician they have.

If there was any doubt about that, it evaporated when Obama chose Castro to give the keynote address at the 2012 Democratic National Convention and launched him as a national political figure.

People should also care because, in the short term, Castro's selection could energize Hispanic voters in time for the midterm elections and help efforts by Democrats to avoid losing more seats in the House or even to retain control of the Senate.

It certainly puts Republicans -- who are already smarting from the beating they took from Hispanic voters in the 2012 election, and who have been trying to make amends -- in a tough spot. If they attack Castro during his confirmation hearing, they'll inflame Latinos who will then turn the GOP into a pinata during the midterms.

Finally, people should care because so much of our politics has become boring and predictable, and this surprise selection -- and Castro's willingness to accept it -- is neither of those things. On CNN's "State of the Union with Candy Crowley," pundits speculated about why a big city mayor would come to Washington midway through the second term of an unpopular administration.

The answer, they agreed, may have something to do with the assumption that it might be hard for a Democratic presidential nominee to tap a mayor for a running-mate position coveted by governors and senators. The thinking is that, if nothing else, moving into the federal arena makes Castro more attractive to Hillary Clinton or whoever the party's nominee in 2016 turns out to be.

The 39-year-old would replace Shaun Donovan, who would move over to take the helm at the Office of Management and Budget.

But why would Castro accept the nomination? HUD is small potatoes. There are four major Cabinet posts: Treasury, Defense, State and Justice. On the prestige meter, HUD is much further down the list. Along with the Labor Department, it is one of those outposts in the federal bureaucracy where the minorities almost always end up in charge.

There is no barrier being broken; another San Antonio mayor, Henry Cisneros, in 1993 became the first Hispanic to be housing secretary. And Castro seems content in his hometown of San Antonio, a base from which he can fly around the country delivering high-paying speeches and where he's finishing a memoir which had been due out next year and which may now be released even sooner. He has never struck me as someone who is desperate to go to Washington.

And yet, now Castro is ready to start packing. The more I think about it, the more I think I understand why he feels compelled to make this move at this point in his political career.

For one thing, Castro knows the subject matter. Big-city mayors deal with housing and urban development, along with economic renewal, on a regular basis. He'll be comfortable at HUD. And it doesn't hurt that, if Castro needs guidance, he can turn to Cisneros, a friend and mentor who knows the department very well, since he ran it for four years during the Clinton administration.

For another, Castro's political options in Texas -- a dependably red state -- are limited. He could run for re-election as mayor next year, and serve out what would be his final term until 2017. Then what? He could enter the private sector, and make a comfortable living practicing law, giving speeches, and writing books. But his political career would be over, just like those of many Texas Democrats before him. His decision to join the Cabinet is a wild card, but one that might just keep him in the game.