pbrower2a,
I think that Americans will vote for a candidate from any racial group, and rightfully so, but I doubt the majority of White voters will vote for a Hispanic candidate because of their background. Should he become the vice-presidential noninee, I suspect Castro could be attacked as a token if he doesn't immediately focus on the issues.
We don't know him that well, do we?
Choosing someone incompetent as a token would of course be a dreadful mistake. Tokens are mistakes as hires or nominations. They usually prove marginally competent at best.
I have no idea how much involvement Julian Castro has had with the Armed Forces. Nobody expects him to know about military policy. Election to the Senate, let alone the House, would have gotten him more access to military policy.
Having had no experience in either House of Congress would be a detriment to him as VP.
Should she be elected Governor of Virginia or a Senator from Virginia, then she goes to one of the three offices (State Governor, US Senator, Vice-President) that one usually needs before becoming President. But Julian Castro is in Texas, and as a Democrat he has no reasonable chance of becoming a Governor or Senator.
Maybe he really is a quick-study, which solves many problems before they can happen. Sarah Palin was definitely not a quick-study.