Trump oversaw several high-profile real estate and building developments in New York City in the 1970s and 1980s, during a time when the city's economic future was dubious and investing there was far from being obviously wise. Trump's projects were often controversial, leading him to become increasingly a public figure, culminating with his construction of Trump Tower in 1983. That was controversial due to its (alleged) questionable taste; the - at the time - dubious business case for such a project in still-then depressed Manhattan; to the demolition of the Art Deco Bonwit Teller building that had previously stood there; and to Trump's increased use of his own name and brand to associate his projects with himself.
At the time Trump was in his thirties, and for an analysis of his type it is useful to take a look at how he came across in interviews of the time. Rather than the later, better known version, who is more inclined to rely on bombast, bragging, self-promotion and extravagant, controversial or even perhaps shocking remarks, the Donald Trump of the early 1980s appeared as a calm, rational, even modest man who showed little emotion or passion as he described in technical detail the reasoning behind his building projects and defended them against criticism, relying on factual, technical arguments (or seemingly so). At the time, Trump started to become identified with NYC's returning optimism since he (by luck or smarts) managed to invest there precisely at the right moment. His public image became that of not only a canny investor but also of a man who "believed in New York", and he explored that image in a virtuous (or vicious) circle whereby his business ventures became indelibly associated with his personality and vice-versa.
In 1987 Donald Trump published his first (and still most famous) book, The Art of the Deal. Actually penned by journalist Tony Schwartz, the book nevertheless is written in Trump's first-person voice and it seems clear that it reflects his own thoughts, words, and views (or at least the views the wanted the public to associate with him). In that book, Trump is still largely his 1980s persona: it is mostly his autobiography (focusing much more on his business ventures than his private life) along with his thoughts, and advice, on how to succeed in real-estate development. That book still reflected what seems to be his obviously deep understanding of that kind of business, as he describes in detail how he came to his decisions, but also with some more general principles: the notions that business deals are about knowing and using one's leverage (F); that intelligence and technical knowledge, or other talents, are less important than one's instinct about their own leverage, strengths, and weaknesses, and a belief that either a person has such instincts, or not (points to F as more valued than P). Further, at the time he was already professing his belief (that later became much more obvious) than even bad publicity is better than no publicity; that making extravagant claims about his objectives and goals, far more than he knows to be feasible, is very useful in building up his image (E blocked with T). He also wrote that another key to success was to always have several alternatives and fall-back positions when trying to strike a business deal, so as never to really lose (points to I). Finally, it is interesting that he seems skeptical of expert technical knowledge when making his big decisions; he prefers, as he says, to ask as many people what they think about a location (especially cab drivers), gradually forming an image of the situation in his mind until he's certain of what the best way forward is (this indicates L as more valued than P in my view).
I argue that the above is perfectly consistent with the core of the present-day Donald Trump, and already reflects some clear Socionics information. His early public persona clearly showed a man at ease with factual impersonal information when defending his business decisions, which was at first obviously a more comfortable "zone" than the appeal to his image. That strongly suggests that his P is in a stronger position than his E. Yet, his increased shift to focusing on E in public, as he got older, more famous and more successful, strongly suggests that E is a quadra value rather than P, which was already clear in The Art of the Deal: P is easy but taken for granted, while E is something he prefers to build up, aim at, and explore. His often-repeated belief that the single most important quality for business deals is to know one's (and others') "leverage", and that is further built up by one's "credibility" which is a consequence of success and the image of being successful, clearly points to F as quadra value and as a zone of great confidence. The above already points to Beta as Trump's quadra - having E and F as quadra values. His strong P points to a logical Beta type, while his focus on keeping several possibilities afloat at once, as well as his confidence in risk-taking and spotting real-estate potential before others shows a reasonable confidence in I. Finally, that Trump states all of that as self-evident truths points to L. All of that already points to SLE as Trump's type, a logical Beta with decent I focus.
"Present-day" Trump presents further evidence. He got into increasingly diverse business ventures that had sometimes little to do with his core business expertise, and were based exclusively on his image, starting with casinos, then into things like Trump Steaks, Trump the Game, finally culminating on the TV shows The Apprentice, Celebrity Apprentice and spin-offs thereof, as well as Miss Universe competitions and the like. I think it's fair to say that by the time of those TV shows he was spending at least as much time (if not far more) in this kind of image-and-celebrity business venture rather than on his originally core real-estate businesses. That again shows the shift from P+F (accumulating wealth through more "concrete" business ventures) to E+F (focusing on his image as a source of power and wealth, as well as probably an end in itself).
Finally, on Trump's most recent "incarnation" i.e. as presidential candidate. His tactics in the Republican primary debates consisted essentially of destroying his rivals through ridicule, by attaching to their images traits (real or not, that's irrelevant) based on perceived weaknesses and pounding on them relentlessly until they "stuck" (i.e. low-energy Jeb Bush (LIE), little Marco, lying Ted, etc). Winning a competition by ruthlessly destroying an adversary, even using what some might call 'low-belt' tactics. shows a focus and skill on F (especially as he himself seemed impervious to such attacks); and the focus on rivals' images - rather than their substance or record - shows again the focus on E, E+T in particular i.e. a broader, longer-term perception of an image, rather than more short-term emotional atmosphere.
Also interestingly, Trump's most notorious political promises are F focused: building a huge wall on the Mexican border (that is the materialization of F), being tough on external commercial rivals, foreign and internal enemies, etc. Whether he actually plans on doing any of that if elected president is less relevant than that he thinks that those promises are effective and plausible and will help him. In addition, the 'present' Donald Trump's focus on E as a political tool has been effective with many people, but they are also seen as over-the-top, or even repugnant, by as many more. This is consistent with E being in a valued function but not really strong (such as lead or creative).
Donald Trump is clearly a SLE and I think it's even difficult to plausibly argue for another Socionics type.
Sources: information on the present Donald Trump is almost infinite; his earlier incarnation can be found in older video interviews and in his first book "The Art of the Deal".
To learn more about SLE, click here.
If you are confused by our use of Socionics shorthand, click here.