"What could Bernie be doing differently, that would actually be effective?"

Unfortunately it's not about Bernie doing something differently. The incremental changes cannot only be made at the ballot box or with candidates. It has to be made within the population at large.

Social movements through collective organizing can bring change. Unfortunately the capitalist state knows this as well and that's why any attempts to organize are stamped out quickly through violence, media campaigns to discredit, or various other means.