Failure doesn't mean you are a failure. . . it just means you haven't succeeded yet. Failure is a detour, not a dead-end street.
That's a question best put to Bernie Sanders himself, but I think that he will probably put forward ideas that are related to the corrupting role of Citizens United and Buckley versus Valeo court decisions and the need to restore a by-and-for-the-people republic envisioned in our Constitution instead of the of-, by- and for-the-most-powerful system that we have right now.