Socialism

Jon Chait has a long history of trolling the Left, but I think he's right about this.  Socialism has - as its endpoint - the state ownership of the means of production.  Democratic socialism wants to get there via elections.  Jeremy Corbyn is a Democratic socialist. 

The Democratic party is a social democratic party.  They want markets, but they want those markets controlled and regulated by the state to varying degrees.  Dysfunctional markets - like the US health care market - require more intervention, as do corrupt markets - the 2007-8 banking/real estate industry.  But the markets for food and basic commodities don't need regulating beyond safety and so forth. 

Chait is also right that the re-interjection of socialism into the debate allows the Democratic party to move left in meaningful ways, by playing off actual proposals to the rhetoric of its more leftward members.