Progressives & liberals form only about 1/3 of the US population in this and most other surveys prospect.org/power/transfor… 
The Sanders campaign theory is that they can afford to alienate almost all Moderates and forfeit many Traditional Liberals because they will achieve historically unprecedented levels of turnout in their favor among the distrustful and conspiratorial Politically Disengaged.
But the thing about the Politically Disengaged is that they are ... politically disengaged!
A certain brand of progressive activist especially covets the Politically Disengaged because they echo the progressive activist's angry accusations against "the system." But it's the dull old Moderates who will show up on voting day even if it's raining.
