It might surprise you but I support the idea of basic food, shelter, education and health care for all and if it had been possible I would have voted for Bernie not Trump. Yes there were other candidates but if the point of voting was to decide who was elected there were only two choices - Trump or Clinton.
You don't think the Democrats represent the left in America and it certainly isn't the Republicans. That's the vast majority of people who bother to register for a party and the vast majority of voting age population that you have ruled out. 
You should be careful with that argument because now the tiny few left are a much smaller pool with which to whitewash/dilute the actions of people like the antifas.