Sanders won't get the same black turnout that Obama got (duh!)
It puts states that Obama barely won thanks to high black turnout in SERIOUS jeopardy:
Ohio, Virginia, Florida (Obama won each by less than 2 points in 2012). Do you really think that someone clearly to the left of Obama would be competitive in those places? That's 60 EC votes right there.
Obama also won
North Carolina in 2008 and barely lost it in 2012... Sanders would get trounced there. Also,
Pennsylvania and
Iowa suddenly wouldn't look so safe.
Sanders' strength is only in deep blue states that will go democratic no matter who gets the nomination.
He doesn't maintain or expand the Obama electoral map, he shrinks it