It's not clear what criteria you're using to judge whether Trump is fit to be President. I can tell from RL's subject line, without reading his post, he's asking a similar question, in his own signature style.

So we now have two points to start to plot the Venn diagram:

1) Being a narcissist (and sociopath and Machiavellian...what psychologists call the "Dark Triad")...nope.

2) Pathological liar...nope. (I don't fling labels like that around lightly. Trump managed to break 2,000 verifiable falsehoods in his first year in office. Whether a given falsehood is a deliberate, conscious lie or not may be debatable, but not Trump's hostility to the truth.)

So, okay, whether #1 disqualifies somebody to be President is surely a matter of degree--when do self-confidence, ruthlessness, and political manipulation skills blend into the Dark Triad? A President must have some of those qualities, but I'm of the opinion Trump is so deep into the Dark Triad that he's crossed the event horizon. But you might disagree.

But lying? We're not talking about the kind of lying sometimes honorably required of a leader; Churchill's deceptions to protect Enigma come to mind. But once again Trump is different: His lies aren't meant to protect the country, they're meant to divide it. His lies are meant to discredit and undermine our democratic institutions, and especially the rule of law. His lies are intended to foment hatred of all kinds, and especially racial hatred. He lies to advance white nationalism. The shithole.

What else might disqualify Trump in your eyes? With enough data points, we can make a graph!