I think I've finally figured out Donald J. Trump. At least I have a basic hypothesis that could be developed into a theory which could be tested. I know I'm a little bit late -- only 4 years -- but they say late is better than not at all.
Sit in a nice sunny window to read this.
(1.) The long con
Let's start with a 26 year old quoted in Reuters:
"If I'm being manipulated by Trump ... then he is the greatest con man that ever lived in America," Caleb Fryar said. "I think he's the greatest patriot that ever lived." 
Given the 2 options Caleb offers I would pick con man instead of patriot. Patriotism is rather a nebulous concept ranging from poor kids with no prospects joining the army in desperation to working class debtors paying their taxes. Neither of those can be applied to Trump and I'm uncertain what else within the category might fit.
In contrast an argument could be easily developed that the con game is characteristic of every stage of Trump's career from rental management through Trump University into the presidency. I don't mean the generic con that is ubiquitous among politicians and common among the discount furniture chains but the classic confidence tricks that Melville wrote about in "The Confidence Man" in 1857: Asking, do you trust me? Will you demonstrate your trust in me? Bringing in a shill to vouch for his honesty. Promises of profit (in Trump's politcal phase profit becomes interpretted as some form of moral superiority). The "hurrah", which is "a sudden manufactured crisis" in the words of Wikipedia. And on down the list.
(2.) Invention over credulity
Trump modified the long con in an important way. (I'd love to know how he discovered this, if he devised it himself, stole it from someone, or just stumbled on it.) Where the classic con hands the mark a scenario and relies on the mark's credulity, Trump induced people to invent their own narrative. In this way the marks are more psychologically invested in the story and less willing to give up their faith in it. We all feel more comfortable if we have an explanatory story. That's why I wrote this essay; I need to make sense of Trump. So does everybody and Trump's brilliance, perhaps his only brilliance, was to turn that need into a weapon.
A side benefit to the success of the con is that discrepencies in the narrative -- or "facts" -- are less a threat than in the traditional con game; discrepencies instead become a challenge to rework the invented narrative to accomodate the additional information. This is also characteristic of conspiracy theories which have become widely popular in parallel with Trump's rise.
(3.) Media and propaganda technique
Donald Trump is not a consumate master of the media but he is undeniably competent as a user of television, Twitter, book publishing, and some other tools. This enabled him to keep his face and taglines incessantly before the public. Repetition and ubiquity are standard propaganda tools known and used by Medicare Advantage Plans as much as by the Trump White House. Consider "fake news", a phrase which means nothing, demands we attempt to understand it anyway, and was so prevalent that everyone was forced to repeat it or become a hermit.
Trump was highly successful in his populist application of the long con but never was able to fool as much as 50% of the people. Close enough to win the presidency one time through the oddities of the electoral college, which is pretty impressive. This may be the first single con which suckered tens of millions of people at once. However, I immediately think of World War I propaganda as a possible contender.
To this should be added the ineptness of Trump's political opponents. The Republicans he steamrollered would be an interesting study. (What ever happened to Ted Cruz?) I'm more attuned to the missteps of the Democrats. In 2016 they nominated Hilary Clinton, a competent person with little sensitivity to the actual concerns of the electorate, and in 2020 they allowed themselves to be self-caricatured through the sloganeering of their natural allies. The most egregious of this latter is "Defund the Police" which was nicely dissected today by Danny Barefoot:
It will be easy for some to dismiss these participants as Trump voters (and they are!) but 70% of them told us they have a negative view of Donald Trump and at some point they supported Joe Biden before ultimately casting their vote for Trump. These aren’t Maga hat-wearing folks.
One of the major takeaways from my discussion with these voters was their distaste for the slogan “defund the police”. While 80% agreed racism exists in the criminal justice system and 60% had a favorable view of Black Lives Matter, only one participant agreed we should “defund the police”. Another participant was exasperated, “That is crazier than anything Trump has ever said.” ...
It is almost beyond parody that progressive activists would build popular consensus on police reform only to slap on a slogan that is deeply unpopular with voters and doesn’t accurately communicate our policy goals. 
Politics is a game played in parallel with the actual reality game. It doesn't have to be a con game, though there are tempting reasons to play it that way. It the end though it is not the political game but the actual reality that matters
•  https://www.reuters.com/article/us-usa-election-trump-fraud-insight/why-republican-voters-say-theres-no-way-in-hell-trump-lost-idUSKBN2801D4
•  https://www.theguardian.com/commentisfree/2020/nov/20/heres-what-interviewing-voters-taught-me-about-the-slogan-defund-the-police "Danny Barefoot is the managing partner at Anvil Strategies, a Democratic consulting firm and advertising agency."