The rich benefit most from politically right policies and the rich are our governing body. If you vote for the most left candidate no matter how far on the right they realistically are then they will just continue to move right because thats what benefits them. I imagine part of your problem is that maybe you view the democratic party as left? It is not, both american political parties are on the right, one is just a little more left than the other. Let me know if this makes sense, i did a lot of work today and my brain is a little fried so im not sure how well i explained that.