For Politico Magazine, I conducted an informal survey of Bernie Sanders supporters to gauge reaction to a possible vice-presidential nomination of Sen. Tim Kaine. The reaction was not good. His support for fast-track trade authority, spending cuts, offshore drilling and personal opposition to abortion (though a pro-choice voting record) all serve to weaken his bond with the progressive populists.
Kaine has risen to the top tier on the presumption that he is a safe choice. But the negativity towards Kaine coming from the Sanders camp means Kaine is not risk-free.
It may be the case that Hillary Clinton's lead over Republican presidential nominee Donald Trump is large enough to withstand some grumbling from the left, but there is a wide range of numbers in the current polling, and several million Sanders supporters still resisting giving Clinton their full backing. If – and it's an if – the race proves to be close, a Kaine nomination may mean lower base turnout, jeopardizing the final outcome.
Other potential nominees, such as Sen. Elizabeth Warren, Housing and Urban Development Secretary Julian Castro, Labor Secretary Tom Perez, Sen. Cory Booker, Sen. Sherrod Brown and Sen. Al Franken, have their own risks too. The lesson for Clinton is there is no "safe" pick. She will have to confront the question of whether she needs to appease the skeptics on her left with a vice president for whom they feel an affinity, or whether she wants to send a stern message that she controls the party's message and direction, not Sanders and his supporters.
Of course, the VP selection is not the only factor that will determine how unified the Democratic Party will be in the fall. The final platform matters greatly, as does Clinton's positions and rhetoric over the next several months. But there's no getting around the symbolism of the VP choice: it is the first major decision of a presidential nominee and it often speaks volumes.
Now Clinton knows what message a Kaine nomination will send to Sanders voters; the question remains if that's the message she wants to send.