Compared to the 2016 primary, one could logically expect that Sanders would do worse this time around. He's that much older, he's suffered a heart attack, he's facing competition not from a single "centrist" Dems like Hillary, but from a lineup of other candidates on a continuum of progressive values.
The fact that -- against all odds -- he's doing so well is meaningful. In the same way that Trump won, despite being so far outside the party norm. All this hair-pulling and gnashing of teeth by pundits and Dem leadership is missing the message. Sanders would not be winning if the Dem party was speaking to the concerns of rank-and-file people. The GOP is a train wreck, but the Dems are cracking pretty ominously, too.
Biden Bros loudly proclaim that only Biden can beat Trump, but if that were true (which I've never believed), then Biden would be handily winning the primary, too. And I have to laugh at all the Wall St. types who were so adamantly opposed to Warren -- happy now? Do you feel safer now that Sanders may be your next president?
On the DU forums, over and over again I have been urged to vote for Biden so that the Dem party could unite. I was supposed to get over not getting my candidate and vote for the larger picture. Well, back at ya. I may not get Warren, but I'll vote for Sanders. And I expect all Dems to do exactly the same or they're just as full of hypocritical partisanship as the Trump supporters, just a different flavor.