Sanders isn't running on a socialist platform or even making his campaign about socialism, so I don't see why anyone thinks that a self-described democratic socialist (and believe me, he's far from actually being one, given that he's not running on socializing even the commanding heights of the economy) running in the Democratic Party primary is automatically going to create space for a socialist wing of the party to emerge. The fact of the matter is that Sanders is running the usual left-liberal populist campaign, and his donors and supporters back that up. He'll get the backing of the AFL-CIO against NAFTA's First Lady and will probably attract some level of support from left-liberal interest groups, but at the end of the day, that's as far as his candidacy goes.
He's a warm up act for Clinton. The only 'legacy' he'll leave is yet another failed left-liberal attempt at capturing the Democratic Party, continuing in the footsteps of Estes Kefauver, Wayne Morse, Eugene McCarthy, Frank Church, Jesse Jackson, etc.
This is assuming, of course, that his goal is actually capturing the Democratic Party. I don't think that's really a safe assumption.
