For Sen. Bernie Sanders to defeat Hillary Clinton in California's June 7 Democratic presidential primary, he'll likely need strong support from independents. But new data suggest the Sanders campaign faces a big hurdle.

Take 67-year-old Paul Taylor, your typical Bernie Sanders supporter: passionate about income inequality, disgusted with the Democratic Party, and a registered independent (or what California calls “no party preference”).

There's just one problem: Taylor's vote-by-mail ballot does not have a single presidential candidate on it.

"I was disappointed as hell," said Taylor, who came from nearby Martinez to watch Sanders speak at a campaign rally in Vallejo Wednesday night. "I really did not realize that I was not going to have an option to vote for Bernie in the primary."

Actually, "no party preference" voters can vote in the Democratic primary -- if they specifically request a Democratic ballot. That's easy enough if you vote at a polling place. But if you vote by mail, like Paul Taylor does, it's a lot harder: You have to submit a form to your county elections office.