I spent a long, awkward weekend with Donald Trump in November 1996, an experience I feel confident neither of us would like to repeat.

He was like one of those characters in an 18th-century comedy meant to embody a particular flavor of human folly. Trump struck me as adolescent, hilariously ostentatious, arbitrary, unkind, profane, dishonest, loudly opinionated, and consistently wrong. He remains the most vain man I have ever met. And he was trying to make a good impression. Who could have predicted that those very traits, now on prominent daily display, would turn him into the leading G.O.P. candidate for president of the United States?

His latest outrageous edict on banning all Muslims from entering the country comes as no surprise to me based on the man I met nearly 20 years ago. He has no coherent political philosophy, so comparisons with Fascist leaders miss the mark. He just reacts. Trump lives in a fantasy of perfection, with himself as its animating force.

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As I’ve watched his improbable political rise, it is clear that he hasn’t changed. The very things that made him so unappealing apparently now translate into wide popular support. Apart from the comical ego, the errors, and the self-serving bluster, what you get from Trump are commonplace ideas pronounced as received wisdom. Begin registering all Muslims in America? Round up the families of suspected terrorists? Ban all Muslims from entering the country? Carpet-bomb ISIS-held territories in Iraq (killing the 98-plus percent of civilians who are, in effect, being held hostage there by the terror group and turning a war against a tiny fraction of the world’s Muslims into a global religious crusade)? Using nuclear weapons? The ideas that pop into his head are the same ones that occur to any teenager angry about terror attacks. They appeal to anyone who can’t be bothered to think them through—can’t be bothered to ask not just the moral questions but the all-important practical one: Will doing this makes things better or worse? When you believe in your own genius, you don’t question your own flashes of inspiration.