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.

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.

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.

The language of the totalist environment is characterized by the thought-terminating cliché. The most far-reaching and complex of human problems are compressed into brief, highly reductive, definitive-sounding phrases, easily memorized and easily expressed. These become the start and finish of any ideological analysis.

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.

There are people who believe that there should be a standard psychiatric examination for every presidential candidate and for every president. But these are difficult issues because they can't ever be entirely psychiatric. They're inevitably political as well. I personally believe that ultimately ridding the country of a dangerous president or one who's unfit is ultimately a political matter, but that psychological professionals can contribute in valuable ways to that decision.

Donald Trump doesn't have clear contact with reality, though I'm not sure it qualifies as a bona fide delusion. He needs things to be a certain way even though they aren't, and that's one reason he lies. There can also be a conscious manipulative element to it. When he put forward, and politically thrived on, the falsehood of President Obama's birth in Kenya, outside the United States, he was manipulating that lie as well as undoubtedly believing it in part, at least in a segment of his personality.