hi clo,
i don't worry so much about that kind of stuff. if he beats hc, the dems will support him in the election. he caucuses with them.
but it's the policies that matter. and he seems to have a fairly standard liberal set of ideas over a long period of time.
a guess. i think he avoids being a party member so he can evade the demands of whips. eg he stands out as someone who voted against the iraq war when nearly all party members were browbeaten into compliance. he wants to vote his conscience, not the current party line.
the party line, it seems, is often set by plutocrats. so this may be why he has such a sympathetic-seeming voting record.
hc, on the other hand, is much more of a party liner and i think this may be the theme of these insurgent candidacies: a rejection of the traditional, controlled party hierarchies in favour of outsiders.
at any rate, when you set aside the "socialist" label, he seems to have ideas which many liberals agree with. and that is what many voters are looking for.
on the other hand, if i find he is going to seek to capture the means of production on behalf of government, then i would be totally disinterested in his candidacy. i'm a mixed economy sort of person. public goods and private property. both. run alongside one another depending upon what is practical rather than what is philosophically ideal.
as you can tell, i don't quite know him well enough to know how far he takes his social agenda.