There are two primary reasons Donald Trump displays less empathy:
1. He probably feels less empathy
2. His forehead is heavily treated with Botox
Since he announced his candidacy for the Presidency of the United States on 16 June 2015, Donald Trump has rarely displayed any expression containing empathy. I've seen maybe two examples after viewing hundreds of hours of video and thousands of images. Of course, I've not seen every moment - and a person may very well display many emotions which aren't photographically captured.
In the image above, Mr. Trump is emphasizing his statement - his forehead is elevating - but his facial expression is not as animated as much as it normally would (and should) have been - because of his heavily Botoxed forehead muscles. We can see that on the far right, lateral edge of his forehead, the muscles are still functional (just above and to the right side of his right eye).
In the image below, Mr. Trump is feeling primarily disgust with some significant anger as well. Although an elevated forehead is not required for either of these emotions, when these particular feelings are strongly, the forehead can be elevated (as it is here). Yet, once again his forehead elevation is only significantly function in its far lateral extreme (this example is seen from Trump's left side).
One could make an argument that a heavily Botoxed forehead would allow a person to display less negative emotions and thus potentially offend less people - and thus, in doing so, project more likability and build more rapport. If this approach is taken, much caution should be used to avoid excessive Botox. When such a procedure is performed, it should only be administered in the area on upper end of the bridge of the nose and just between the eyebrows. When higher regions of the central forehead are treated with Botox, it inhibits our ability to express many emotions - and perhaps the most important of these is empathy. Empathy cannot be anywhere near adequately expressed without an elevated central forehead contraction.
Summary: Heavily or moderately Botoxed forehead muscles very significantly inhibits our ability to express a myriad of emotions. Not being able to display these feelings prevents our ability to adequately communicate. Building rapport and likability are profoundly important qualities for every human being - particularly when leading a country. President Elect Trump: Less Botox = More Influence.
Nonverbal Communication Analysis No. 3754: Donald Trump, Mike Pence and Paul Ryan at the US Capitol
Nonverbal Communication Analysis No. 3752: Barack Obama's and Donald Trump's Handshake
Nonverbal Communication Analysis No. 3750: Bill's Reaction to Hillary Clinton's Concession Speech
Nonverbal Communication Analysis No. 3725: Donald Trump Challenges Hillary Clinton to a Drug Test before Debate
Nonverbal Communication Analysis No. 3712: Lloyd Bentsen to Dan Quayle - "You're No Jack Kennedy"
Nonverbal Communication Analysis No. 3707: The Presidential Debates Part III - Donald Trump v. Hillary Clinton and Sniffing
Nonverbal Communication Analysis No. 3664: Benjamin Netanyahu, Viktor Yanukovych and Vladimir Putin
Nonverbal Communication Analysis No. 3615: Store Owner Abdullah Muflahi Interview regarding the Shooting of Alton Sterling
Nonverbal Communication Analysis No. 3578: Megan Fox, Body Language and Dismissive Emotions