From Max Ehrenfreund, Why Bernie Sanders’s strategic gambit may not be as unreasonable as it seems:

Sanders’s strategy… won’t be to run to the left of Clinton… His campaign won’t be about mobilizing the party’s left flank or its base, its highly educated members living in coastal cities. Instead… his goal will be to appeal to working-class white voters, many of whom might describe themselves as moderate or even socially conservative in surveys…. Sanders… likes to talk about how he consistently wins by large margins in his home state, which shows that he has in fact won the allegiance of many otherwise conservative voters. [Ed.:  Sanders’s electoral history here.] His supporters, possibly, feel alienated from the political and financial elite that makes up the establishment in both parties. No Democrat represents that elite better than Clinton.

Sanders’s policies will be to her left, but in his view, his constituency will be to her right. The real question for him is not about the strength of his support among committed liberals, but whether he can persuade moderate Democrats outside of Vermont to vote for him…

If Jim Webb is going to make a serious run then that’s the approach he needs to take:  appeal to people who are alienated from the political and financial elite.   The challenge is that many of those people don’t vote.  How does Sanders (or Webb) convince them that it’s worth their while to do so?