At home, Julián Castro’s been spending more time reading and watching television in Spanish, trying to get his speaking skills up to speed.

On the job as Housing and Urban Development secretary, he’s been carefully working the levers in Washington, with coaching from Bill Clinton and a twin brother who’s a popular and up-and-coming congressman himself.

Starting Saturday, he’ll be out on the trail for Hillary Clinton in in Nevada, Iowa and Maine.

He’s plotted his rise carefully, studying and strategizing with a clear goal in sight. But if Clinton picks him to be her running mate, it’ll be more about perfectly fitting his party’s moment and the nearly non-existent Democratic bench than about his 18 months as a HUD secretary who hasn’t left a deep mark at his agency, the White House or the housing world.

Castro’s got a made-for-campaign commercials biography, and an undeniable savvy that’s helped him spin a job as a part-time mayor of San Antonio into an unusually successful 2012 Democratic convention keynote and then the answer to the second term Obama White House’s own search for more diversity in the Cabinet, without having to wait until he could win statewide in Texas.