Bernie Sanders is the prophet with honor in his own party. The former socialist gadfly is now the socialist trendsetter. At the moment, he has to be counted among the most successful ideological leaders in a generation in terms of moving the terms of the American political debate and putting previously discounted ideas on the agenda.
This doesn't mean that he'll be the next Democratic nominee for president, or even run. It doesn't mean that his ideas are good (I personally consider them godawful). It does mean that when it comes to domestic policy on the left, it's Bernie's world, and the rest of the Democrats live in it.