The betrayal of the democratic process, and the working class, within the Democratic party has been an ongoing process since before the 68 convention fiasco. The competition between the parties for voters shifted to a competition for donors after the Kennedy administration. As a result, America has been dragged, mostly in its sleep, so far to the right that Eisenhower would now be viewed as a far left Marxist. The effect of this has been tens of trillions of dollars shifted away from workers and into Cayman Island accounts of the elite of Wall St and the bankrupting of millions of Americans that no longer even expect a voice in their government. They have opted for shifting their own ideology to match that of their chosen party simply to avoid believing that they have lost all control of their nation.
When polled on issues separately, they align with the positions taken by Bernie about 85/15, but their political choices show barely 50/50 split because neither party reflects their best interest. It would have been easy for the DNC to simply adopt the more popular positions and sweep the election, except they looked at the model of politician that Bernie represented and wanted no part of that. Thirty years of service in politics and still worth less than a million? The consensus among the establishment Democrats comfortable in their districts with little concern for anything like progressive policy or actual democracy was that Trump couldn’t be all that bad as a second choice for President.