"Julián Castro seems entirely comfortable expressing views on national and international matters normally outside the purview of first-term mayors. He and his identical twin, Joaquín, are scions of the west-side barrio political machine their mother helped build, and they were raised with the expectation that they would be leaders, young men of personal excellence and public spirit. They were the undisputed stars of Jefferson High School, where they played on the tennis team, earned top grades and skipped 10th grade. In their spare time they accompanied their mother to political events and strategy sessions, where they were exposed to her fiery style of radicalism (which, in any case, was softening over time); met the key figures in the Chicano political world; became practiced community organizers on political campaigns; and learned to make the system work for them.
A place on the San Antonio City Council doesnt come with a salary, and the Texas State House of Representatives, which meets only 140 days every two years, pays what averages out to be about $16,000 annually. The Castro brothers already had day jobs at the local branch of Akin Gump Strauss Hauer & Feld, a major law firm with offices around the world. Later they started their own practice. A celebrated personal-injury case, in which they represented victims of a fatal drunken-driving accident, earned them enough to comfortably continue their political careers."...... Source
And I fully expect Julian Castro to run for Texas Governor sometime in the future. Julian was elected mayor of San Antonio with the support of the Anglo north side. He's a liberal Democrat but has been careful to not appear overtly radical.