You don't need to move 51% of the population to get some action. You just need to impress those Congressmen with a few thousand contacts all pushing the same issue.
While I agree with you that democrats need to go for it and do politics that last comment has little evidence to support it.
Oh wait. Gay marriage.
I can think of little else done for the average american in the last 25 years that has had much of a positive impact on peoples economic or political lives in a real, tangible way.
Forget about a green new deal or a 'Fight For 15', Medicare for all, etc etc etc.
Democratic Neoliberalism, to borrow an anology, is like nailing jello to a wall.