Donald Trump, the establishment candidate

In a traditional context, political fame is achieved through demonstrated success in national office or in a previous campaign. The media then tends to cover these candidates more, granting them further legitimacy. This was the Romney or McCain model.

We now know that when this fame is established outside the traditional channels, and also proves too big a draw for the media to resist, the model utterly breaks down. (Perhaps Arnold Schwarzenegger was the canary in the coal mine for this.)
It also means that our idea of what an establishment candidate is, and how they gathered support in previous elections (our mental frame of reference when planning for this election) is completely wrong.

In the minds of the political class, Romney and McCain voters opted mindfully for sober, responsible, center-right candidates who could win the general election. This is the story that Republican establishment donors, operatives, and consultants tell themselves.

But in reality, many voters prefer big personalities and obvious choices. A big personality was why George W. Bush was the last truly successful national Republican leader, and of course, why Ronald Reagan was before him.