Yes, Trump is inarguably a psychopath. And a dangerous one.

Note: this post is based mostly on a long article by Dr. Vince Greenwood, a clinical psychologist who founded the site DutyToInform.org because he is alarmed by Donald Trump. Greenwood directly addresses the so-called "Goldwater Rule"—you can't diagnose psychological disorders without interviewing the subject personally—and why it doesn't apply to Trump. I highly recommend the entire article, but this post covers the key points about Trump. 

Thesis: The 45th President of the United States has a disorder that conveys danger to all those in his orbit.…There is no cure for this disorder. Nor do there appear to be any effective measures to curb it. The best we might do is diagnose the disorder and warn others.

Psychopathy has received more attention and research than any other personality disorder, with over 3,300 studies to date. One can predict with a high degree of confidence that a person diagnosed as a psychopath (about 1% of the population, 75% male) "is destined to inflict significant harm and mayhem on many that cross his path." 

The standard Hare Psychopathy Checklist consists of 20 traits, each to be scored a 0 (not present), 1 (data unavailable or inconclusive), or 2 (definitely present). Traits include the following (see the article for the complete list): 

• Egocentricity/grandiose sense of self-worth 
• Pathological lying and deception/gaslighting 
• Conning/lack of sincerity 
• Callous/lack of empathy 

A "perfect" score on the checklist is 40. Different researchers have used either 25 or 30 as the threshold for a clinical diagnosis of psychopathy. The average score among the general population is 5. Among imprisoned criminals (male), the average is 22. Greenwood calls a score of 30 or more "extreme and dangerous".

He gives Trump a score of 32. 

To a significant degree, psychopathy is inherited, suggesting that Trump's parent(s) may well have suffered from it. As to what exactly is being inherited, recent research has established that it's a different brain structure than most people have. Briefly, psychopaths process emotionally-charged situations in the part of the brain responsible for language and problem-solving, not the part that handles emotional regulation. "They simply do not experience the appropriate emotional reactions to moral wrongs." When you think of a "cold-blooded killer", he's almost certainly a psychopath. 

The psychopath's brain also doesn't respond normally to things like fear of violating acceptable rules and boundaries, and the regions responsible for impulse control are smaller.

In a nutshell, then, Donald Trump inherited a brain that doesn't work the way most of ours do. He is literally incapable of caring or empathy. 

These brain anomalies "help explain three fundamental traits that appear to be foundational to the condition" of psychopathy: 

1. lack of conscience 
2. inability to process emotions that foster empathy and human connection
3. inability to control impulses
   

Author Martha Stout paints this picture of the psychopath in her 2005 best-seller, The Sociopath Next Door: 

Imagine—if you can—not having a conscience, none at all, no feelings of guilt or remorse no matter what you do, no limiting sense of concern for the well-being of strangers, friends, or even family members. Imagine no struggles with shame, not a single one in your whole life, no matter what kind of selfish, harmful, or immoral action you have taken…Now add to this strange fantasy the ability to conceal from other people that your psychological makeup is radically different from theirs. Since everyone simply assumes that conscience is universal among human beings, hiding the fact that you are conscience-free is nearly effortless…You can do anything at all, and still your strange advantage over the majority of people, who are kept in line by their conscience, will most likely remain undiscovered.…you pursue your career with a cold passion that tolerates none of the usual moral or legal encumbrances. When it is expedient you doctor the accounting and shred the evidence, you stab your employees (or your constituency) in the back, tell lethal premeditated lies to people who trust you, attempt to ruin colleagues who are powerful or eloquent, and simply steamroll over groups who are dependent and voiceless… You have a special talent for whipping up other people’s hatred and sense of deprivation… And all this you do with the exquisite freedom that results from having no conscience whatsoever…You become unimaginably, unassailably, and maybe even globally successful. Why not? With your big brain, and no conscience to rein in your schemes, you can do anything at all.

Greenwood continues (emphasis added): "It’s hard to imagine having no fear about being found out for moral transgressions, no compunction about lying, and no gut-level reservations about acts that might harm others.…Conscience is the glue that keeps the social fabric from unraveling. It undergirds the social contract that promotes decency, safety, and trust. Yet there is that small percentage that live outside that social contract… Is it not desirable to identify those without a conscience, particularly if they are in a position of power over others?" 

And "the psychopath has plenty of emotional fuel. Admittedly, not the animating force that flows from love, compassion and empathy; but emotions associated with the drive to dominate such as anger, glee, resentment. envy, consternation, jealousy, and contempt. These emotions are shallow and often fleeting, but can be intense in the moment, and typically drive the psychopath’s behavior." 

Sound like anyone we know? 

A few additional points gathered from the text: 

• For the psychopath, life is ruled by impulse. 
• When an impulse is triggered, the deficiencies in higher-level mental functions means there is no counterweight to it. 
• The calls most of us make every day between “l want” vs. “l should” just don’t take place with a psychopath. He has only one play available to him: the short game of winning the moment. 
• Elizabeth Stout emphasized the psychopath’s inability to develop a loving bond with another. David Shapiro would argue there is a more fundamental inability to develop any deep allegiances: to a significant other yes, but also to friends, the community, even ideas and values. 
• The pathological liar often contradicts himself within minutes (but shows scant concern for the contradiction). The psychopath is not interested in what is being said, but how it works for him.
  
• He is at the mercy of saying quickly whatever meets his egocentric needs of the moment. 
• Psychopathy is a unique form of psychopathology in that it does not involve suffering by the psychopath himself. The main consequence of the condition involves the danger it poses to others.
  

"For a psychopath who is in a position of significant power and authority, other manifestations of his condition bode ill for those under his sway. These would include the inability to act predictably, the inability to react calmly and without aggression, the inability to examine his own behavior and accept responsibility, the inability to respect boundaries and limits, and the inability to place the interests of others or the common good above his own." 

This is getting long, but I want to mention a few additional points Greenwood addresses: 

• Trump is often called a "malignant narcissist" (combining narcissism, sadism, paranoia and psychopathy). While this may be an apt description of him, it is not a formal, accepted diagnosis, and is unnecessary. 
• Trump is often called a "sociopath", a term often used interchangeably with "psychopath". The latter is the correct scientific term. 
  
• While Trump exhibits narcissistic behavior, there is a difference. Narcissism is “hot” (the heat of feeling vulnerable) underneath, psychopathy is cold. One is an insecure peacock, the other a snake. The narcissist breaks rules because he feels special and entitled. The psychopath breaks rules because he wants to secure an advantage. 
• There is one feature of Narcissistic Personality Disorder that applies to Trump and may contribute, at the margins, to his dangerousness. Narcissists are triggered by perceived criticism, which they view as attacks on their self-esteem or status. That can lead to aggressive outbursts and rash decision-making.
  
• Psychopaths are extremely good at hiding their condition and making others believe them. They exploit the human tendency to accept what others tell them at face value. 

There is much, much more in the article. The conclusion is inescapable: Donald Trump is a psychopath, and he is very dangerous.