One reason that I embarked on a study of Nazi doctors was that in this personal journey, I had the feeling increasingly that I did want to do a Holocaust study and that increasingly I wanted it to be of perpetrators, which I thought was more needed.

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.

As a kid I was fascinated with sports, and I loved sports more than anything else. The first books I read were about sports, like books about Baseball Joe, as one baseball hero was called.

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.

Donald Trump gives the impression that he would like to govern by decree. He has that impulse in him and he wants to be a savior, so he says, in his famous phrase, "Only I can fix it!" That's a strange and weird statement for anybody to make, but it's central to Trump's sense of self and self-presentation. And I think that has a lot to do with his identification with dictators. No matter how many they kill and no matter what else they do, they have this capacity to rule by decree without any interference by legislators or courts.

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.

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.