to share your position. By the time one runs for president they already stuck in their position. Unless you find a candidate that is already 'left' of center you're not going to get it once they are elected.
You can demand all you want it's just not going to happen,see our speaker of the house etc. They'll tell you what you want to hear and in the end they will do what they want to do because they just don't give a damn!
Well that's my opinion anyway.