From one VP to another? Vice President Biden and then-San Antonio Mayor Julian Castro chat in Iowa in 2013. Castro is on Hillary Clinton's vice president watch list. (Steve Pope/Getty Images)

When it comes to Hillary Clinton's  private e-mail server, many Democrats have kept their mouths shut. Many, but not all.

Over the weekend, Secretary of Housing and Urban Development Julian Castro defended Clinton’s use of a private server to house her work e-mails as secretary of state, calling criticism over how she handled the situation “a witch hunt.

Allow us to translate: “I’d be a great attack dog for you as your vice president, Hillary.”

Castro is already likely on (or on top of) Clinton’s veep list, which -- wink, wink -- doesn't exist. Castro has a resume that seems tailor-made for higher office in 2016: He’s a former San Antonio mayor, a Harvard Law grad, was named in 2010 to Time Magazine’s “40 under 40” American political leaders and has the Hispanic pedigree that might round out a Democratic ticket nicely. (Fun fact: He doesn't speak Spanish.) His twin brother, Joaquin, is a congressman from Texas. Obama even made a joke about the twins during April’s White House Correspondents' Association dinner.

Still, defending Clinton’s intensely private use of her public e-mail account is no easy matter. Party leaders such as Barack Obama (he's the president as you might have heard) and Senate Minority Leader Harry Reid (Nev.) haven’t jumped to support her, even as Clinton calls on the State Department to release 55,000 pages of her e-mails as soon as possible.

Of particular interest in those e-mails to congressional Republicans: Nine-hundred pages released Friday that show she received sensitive material on her questionably secure private server during the 2012 attacks on two U.S. compounds in Benghazi, Libya, that killed four Americans, including U.S. Ambassador Chris Stevens.

On Sunday, Castro used the Benghazi investigation to try to turn the tables and point the finger at Republicans. He aimed to cast South Carolina Republican Rep. Trey Gowdy, who is leading an investigation into how the Obama administration handled Benghazi, as a boogeyman. “This thing has been studied to death by Republicans and Democrats,” Castro said. “… And Congressman Gowdy, who is leading this, is very intentionally trying to manipulate this witch hunt to play politics.”

Polling shows Democrats -- not surprisingly -- agree with Castro: In early March, as criticism reached a crescendo for Clinton’s handling of her e-mails, her favorability in a Gallup Poll was at 79 percent among likely Democratic voters, higher than last year.

Castro may be onto something by trying to tie Clinton’s larger e-mail problem to Benghazi. He joins others in his party, such as Rep. Elijah Cummings (Md.), the ranking Democrat on the Benghazi committee, in crying foul for Clinton. “Unfortunately, it appears that the Select Committee on Benghazi has now become a taxpayer-funded effort to damage Hillary Clinton’s campaign for president,” Cummings said.

But Castro’s attempt to turn voters’ attention to Gowdy could prove difficult: A June 2014 Gallup Poll as Republicans launched yet another investigation into the incident found a majority of voters -- especially independents -- aren’t paying much attention to the scandal anymore.

So overall, how did Castro do as his first tryout as veep? He got a few headlines, and he certainly didn’t create any more trouble for Clinton on the issue. Maybe that’s all she can ask for in a vice president.