A quote from his blogpost, the link above:
In entering the Trump era it is the movement that Sanders was part of coalescing that becomes key in building a resistance that has a positive vision. One of the weaknesses of the Sanders message was its failure to unify matters of class with race and gender. This is not an academic exercise. This is about telling the right story about what has been happening in the USA. It is also a matter of taping into significant social movements, e.g., Occupy; immigrant rights; LGBT; environmental justice; movement for Black Lives. These are movements that are focused on the future and a future that is progressive. This, in fact, is where the hope lies.