Should Sanders Fight Trump, Not Clinton?

A group of Bernie Sanders supporters have drafted a proposal for Sanders to bow out of the campaign after the June 7 California primary, concede the nomination to Hillary Clinton, and then campaign against Donald Trump. His supporters believe that Sanders will win the California primary but not the nomination. The supporters who drafted the proposal do not have authorization from the Sanders campaign. The proposal takes a longer view. Rather than just duke it out at the convention, the supporters are focused on building a independent organization focused on change harnessing the energy of new activists. Should Bernie take the long view?