The problem with being an independent, is that, in most states, you are not able to vote in either party’s primary. As a result, what you have remaining, are extremes, and in order to get elected, you need to appeal to the party extremes. What comes to mind is Mitt Romney’s statement from the 2012 campaign when his answer to a reporter’s question was “… I’m a severely conservative governor!”. Seriously? First, no severe conservative gets elected governor of Massachusetts, and this is the governor that sponsored and passed Romney Care (Mass Health) that the Affordable Care Act was modeled after. Romney may be a lot of things (and I voted for him), but he is not a conservative. I would classify him as slightly right of center, which according to CNBC, is where most Americans views fall.
However, candidates will sometimes do whatever is necessary to get elected (within legal boundaries), and as a result each party has been nominating extremes. If you look at the past democratic nominees, they don’t get any more liberal than Kerry, Obama and while I don’t consider Hillary an extreme liberal (at least from her voting record as a Senator), she is talking the talk.
And as for Trump, I think it’s fair to say that he gives extreme new meaning.