Is there a historical parallel for the upcoming presidential election?

It seems like an unprecedented dissatisfaction with politicians in general along with a weak field of candidates are leading to candidates that are the furthest to each side of the spectrum that we’ve seen.

The candidates leading most of the news right now are way out there by US political standards, and seem to be (at least at this very early point) leading the way in terms of message. It’s almost to the point where more traditional candidates seem to be ready to join in with a little showmanship to get a mention.

Has this happened before on this scale? If so, when? How did it turn out?

If it’s something new, does it mean we’re in for an even wider rift between the two leading parties going forward? If so, will there be anything to fill the middle ground?

Just to clarify: Trump, Sanders, and Carson are the candidates that lead to the question, but it almost seems if they weren’t there, someone else just as far out would be. All would historically be considered “unelectable” I think.

I understand Clinton is leading in polls, but generally has to pull a circus stunt to get a news mention.