I don’t know what to think about this.
IMO he's right but also wrong. He's absolutely right in that Hillary being further ahead in the swing state polls at this point in 2016 than Biden is, is a bad look, and in that respect Dems should be concerned.
But as much as I'd personally prefer for the Dems to go further left, he doesn't give any good evidence that it would necessarily help them win against Trump. I feel like a lot of people are just in denial about the fact that social/cultural issues motivate voters more than economic ones. It's stupid but there have been many studies on the subject showing that's the case.