Bernie Sanders who is running neck and neck with Hillary Clinton for the Democratic presidential nomination explicitly ruled out ever joining the party, documents show. 

Mr Sanders outright refusal to consider becoming a Democrat emerged in the archive of his papers at the University of Vermont in Burlington, the town he served as Mayor from 1981-89.

The independent socialist Senator for Vermont made his feelings clear in a letter written in July 1988 - during his first, unsuccessful congressional run - to Derek Shearer, an academic at Occidental College, Los Angeles, who also served as US ambassador to Finland.