Why did Bernie Sanders fail?

In the third in an occasional series on the US presidential election and the Left, we talk to Angela Nagle and Michael Tracey about their analysis of Bernie Sanders' campaign. We put to bed some bad arguments as to why Bernie didn't win the nomination, and examine some better ones: was the campaign was too establishment-friendly? too "left"? too middle-class? too anti-nationalist?... or are structural factors to blame instead?

And we ponder the end of the union of Old and New Lefts, of cultural liberalism and socialism. And the most worrying of all: was Bernie just a blip?
Reading:
First as Tragedy, Then as Farce: The Collapse of the Sanders Campaign and the "Fusionist" Left, Angela Nagle & Michael Tracey, American Affairs