The 538 Elections Podcast (which, if you don't subscribe to, you should consider adding to your podcast catalog) did a retrospective on the GOP primary thus far which included a discussion of the various candidate's "theories of the Republican Party." Rubio essentially holds that the party hasn't changed that much, Cruz that it's gotten a lot more conservative since 2012, and Trump... well they didn't seem to have an answer for that.
"He can manipulate the media" and in so doing secure the nomination was as close as the 538 crew got to pinning down what makes Trump tick and, bright as Nate Silver's team is, they seem to have completely missed what's driving the Trump campaign.
And it's obvious.
Open up a new tab real-quick and head on over to Facebook. Scroll through your feed and find the first five posts that clearly espouse a conservative ideology. I'll wait.
Got them? Good. 4 out of 5 of them amount to "Liberals are dumb," "Liberals want stuff for free," "Liberals are wimps and get their knickers in a twist when someone does/says/thinks ________."
It's not that conservatives don't have ideas or that they don't believe in those ideas, but the policies that have defined the conservative movement for the last thirty years or so aren't exactly aspirational. Save for the veneration of the military, conservatism has been about "the country would be great if ____— stopped happening" and that's very hard to turn into something with real emotional resonance. The only real way to appeal to a positive emotion with that kind of message is to make light of the people who believe the opposite. To insult them, demean them, pick on them.
That's politics - if you can't take the heat get out of the kitchen - but the result of this being the dominant messaging of the Republican party for three decades is an electorate that thrives on a bombastic, aggressive demagoguery, on insults, crassness, and base rhetoric.
And Donald Trump has that in spades, always has.
So what's Donald Trump's theory of the GOP? It's that the Republican Party has become his kind of people - not necessarily more conservative or less but hungry for validation of the virtue of being an outsider in the world of identity politics, tolerance, and open-mindedness.
He might be right.