Is "candidate for President of the United States" a different role from "President of the United States"?

Trump chief: ‘You’ll see a real different guy’

I find this a really interesting idea.
At first glance, I was mildly outraged that “President of the United States” could be considered another “role” to be played like another reality TV show.
But is it really that preposterous? Since the 70’s and the dominance of TV in American lives, how many candidates have gone on to be the President they promised?

On the other end of the spectrum, does anyone believer President Sanders would have the authority or clout to achieve free universal college tuition? Or is that part of his “role” as candidate?

Is Trump, the non-politician, inadvertently showing how little difference there is between modern American politics and modern American reality TV?