Now just to be clear: Trump hasn't actually resigned. But he has abdicated the moral authority inherent in the American presidency this past week.
Trump constantly and consistently puts himself before the country. Rather than try to bring the nation together after Charlottesville, as all other modern Presidents would have done, he is interested only in fluffing his fragile ego.
The man cannot admit he is or was ever wrong. So he keeps doubling-down, like a spoiled child, insisting he's the best, he is right, that he knows everything, not caring a whit about the damage that may be done to America and its people.
Like all extreme narcissists, the man has a monumental ego to accompany his relative mediocrity.
Read Bruni's piece. It's a fast and great read. While it's not really relevant, in case you didn't know already, Bruni happens to be openly gay.