It has been demonstrated time after time that the support of white liberals alone is not sufficient to get the Democratic Party nomination. I strongly suspect that Elizabeth Warren decided not to run largely because she is aware of that fact. The Sanders candidacy is ultimately doomed because it has no appeal to the rest of the party.
I think it would be very useful if the Democrats had a candidate who would discuss the need to rethink and rework the welfare state in light of technological change (i.e., the “gig economy”) and globalization. For example, does it really make sense in today’s world to tie the cost of Medicare and Social Security solely to the payment of wages? And is it a good idea for Obamacare to include an employer mandate? Sanders is too tied to the past to have this discussion.