I agree Becerra strictly dominates Castro as a VP choice for Clinton. He's also the child of undocumented immigrants which would make his life story even more interesting. Other options:
Generic Obama Coalition Dems ("Safe" picks):
Kaine: Probably the strongest in this category- early Obama endorser + history of winning VA + speaks Spanish+ D Gov to appoint successor. He also retained greater white working class support than Obama (albeit against a weaker opponent). He's not particularly young and there's the whole vulnerable 2017 special election thing, though.
Heinrich: Young + widely considered handsome + from a diverse former swing state + environmental activist cred. The major downside is Martinez would get to R+1 an otherwise Likely D seat.
Hickenlooper: Only Dem governor reelected in a swing state in 2014 + passed Walker-style aggressively partisan state agenda during 2013-14 trifecta and lived to tell about it + gun control cred. He's implemented Obama's entire 2nd term agenda in a swing state, something basically no one else has yet accomplished and retained some moderate cred while doing it. Of course, he's also a 63 year old white guy.
Klobuchar: mainstream left woman + landslides in lean D MN + help with midwestern swing voters + D Gov to appoint successor Downsides: not charismatic + doesn't add anything novel to ticket
Latinos
Becerra: Proven political success + presumably already heavily vetted by former opponents + aggressive progressive + powerful life story. Downsides: from CA + would be very polarizing + not young
Castro: Young + unique (1st mayor as VP) + background. Downsides: very untested politically (Palin risk) + has made substantial gaffes in the past + from TX
Populists
Warren: aggressive progressive + great at fundraising + help with base turnout + woman with compelling life story. Downsides: the whole fake Indian controversy + potentially too far left for many swing voters + from MA + R+1 in senate from normally safe D state (but veto-proof legislature could prevent this
Bullock: held conservative-trending ancestrally D state + worked with R legislature to get Medicaid expansion + considerable white working class appeal. Downsides: The whole John Walsh thing + likely R pickup of governorship + untested outside of small, idiosyncratic electorate (some Palin risk)
Warner: repeatedly successful in VA + D Gov to appoint successor + moderate populist persona Downsides: nearly lost in 2014 after coasting + white working class appeal may have evaporated + seat not up until 2020 if he stays in Senate + pretty much strictly dominated by Kaine now
Manchin: has uniquely strong white working class appeal + held ancestrally D right trending state during 2010/12 + tried for gun control in very inhospitable place + can retire in December to assure D appointee Downsides: likely too conservative for national D's + very independent streak from national party (if senate was 50/50, he would probably break some ties for Republicans) + turnout risk from environmental groups
Then there's the remote possibility of a coup de grace like getting Sandoval or Martinez to switch parties after Trump clinches the nomination, but beyond that scenario, there's nothing to gain IMO from choosing a Republican/former Republican.
I want to see Kaine, Warner, Manchin, Becerra on the ticket. Becerra would be the ultimate pit bull attack dog. Rubio or Haley would be destroyed in a debate with Becerra. Thune can debate Becerra with style.
