He's right but I feel like the Dems are too scared to go fully progressive because of the social climate of the US. The heart of this country isn't interested in progressive, socialist types of politics on a grand scale; too much hate, bigotry, disdain, and a desire to see certain people suffer/lose is why these types of politics don't go far and are partially why the Dems lost in November.
It's like I've been saying: progressive political policies are a losing strategy for Dems because, unlike Republicans, they can afford to go fully Far-Right/ultra-conservative. After all, much of their voting base supports that type of rhetoric/agenda, so it's easier to get things done and not be scared of alienating a segment of their supporters.
Dem voters are split between being moderate/centrist (somewhat liberal, somewhat conservative, y'know 50/50) and progressive beliefs (social justice reform, gender, race, etc).