In early psychoanalytic thought, narcissism was - and still, of course, is - self-love. The early psychoanalysts used to talk of libido directed at the self. That now feels a little quaint, that kind of language. But it does include the most fierce and self-displaying form of one's individual self. And in this way, it can be dangerous. When you look at Donald Trump, you can really see someone who's destructive to any form of life enhancement in virtually every area. And if that's what Fromm means by malignant narcissism, then it definitely applies.

With the nuclear threat we know that if sufficient weapons are used, human civilization - all of humankind - could be extinguished literally by "nuclear winter." So we have to see ourselves as part of the ultimate human group, just as we have to do with global warming.

Trump has a mind that in many ways is always under duress, because he's always seeking to be accepted, loved. He sees himself as constantly victimized by others and by the society, from which he sees himself as fighting back. So there's always an intensity to his destructive behavior that could contribute to his false beliefs.

People with what we call mental illness can indeed serve well, and people who have no discernible mental illness - and that may be true of Trump - may not be able to serve, may be quite unfit. So it isn't always the question of a psychiatric diagnosis. It's really a question of what psychological and other traits render one unfit or dangerous.

While Donald Trump doesn't have any systematic ideology, he does have a narrative, and in that narrative, America was once a great country, it's been weakened by poor leadership, and only he can make it great again by taking over. And that's an image of himself as a strongman, a dictator. It isn't the clear ideology of being a fascist or some other clear-cut ideological figure. Rather, it's a narrative of himself as being unique and all-powerful. He believes it, though I'm sure he's got doubts about it.

The American president has particular power. This makes Trump the most dangerous man in the world. He's equally dangerous because of his finger on the nuclear trigger and because of his mind ensconced in solipsistic reality. The two are a dreadful combination.

I did the first study because I had been exposed to something that I took to be important and interesting - this thought reform process - in the military.