I don't really buy it. Donald Trump can't win a general. The big secret about these primaries is that very few people go to these things and they are often not representative of either parties interest in the state. The people that come out to primaries and caucuses are the really politically involved. The reason Donald Trump is doing so well is because it is super easy to get the outliers all to vote at one time, and the general populace tends to be more apathetic to this early election stuff. The general election for a presidential candidate is a whole different beast. I'm pretty confident Clinton or Sanders could beat Trump in a general if not from just the sheer amount of disgust for Trump.
Exactly. In the primaries you're appealing to roughly 50% of roughly 97% of the electorate that has made up its mind and will never vote for the other side's candidate. In the general you're trying to grab the 3% that's legitimately up-for-grabs, doesn't hear your dog whistles, and has somehow managed to stay undecided in the most polarized political climate since the Civil War.
Every election is a few points off of 50/50. Nobody gets a "mandate" any more. So the driving is done by those who give a shit and show up to caucus. Then the PACs use their money to influence the media we proles are exposed to every day, and make a certain outcome seem "inevitable", so we'll just sheeple along with their message and vote the way they want us to. It's the 3% of undecideds that sway every election. But... when do they Decide? And how can we influence them? I think that answer is "Big Media Buys", but only in the three states that ever matter. Which includes Florida. Which means we are all fucked.