I think they think they can prop Obama by dropping Biden ad putting Hillary on the ticket.
Someone else is trying to steal that thunder, though my source may stand corrected;
http://en.wikipedia.org/wiki/United_States_third_party_and_independent_presidential_candidates,_2012
Stewart Alexander, Activist and 2008 Socialist Party USA vice-presidential nominee of California
According to a published report, Alexander “says his intentions to seek the presidential nomination (of the SPUSA) is based upon ..... addressing the needs of the working class, creating good paying jobs, protecting human rights, protecting the environment and ending the U.S. occupation in Afghanistan and Iraq.”