I have seen this week that Sanders supporters think that Sanders is viable because"
1. The Democratic blue wall is magical and will work for anyone with a D behind their name even in they are not in the mainstream or if they are not adequatedly funded.
2. Twitter is magic
3. Social Media is magic
4. Youtube is more important than tv advertising and Hillary Clinton is not as comfortable on youtube as Sanders
5. Money is evil and so does not matter in politics.

The magical thinking of Sanders supporters as to his viability in a general election where the Kochs are spending $887 million and the RNC candidate may spend another billion dollars is amazing. Sanders is not broadening his base beyond the current limited base because many Democrats do not think that Sanders is a serious candidate who can run a viable general election campaign. I doubt that Sanders can broaden his appeal without convincing Democratic voters that he is viable