David Frum deals with it at greater, more eloquent, length:
Trump’s perfect emptiness of empathy has revealed itself again and again through his presidency, but never as completely and conspicuously as in his self-flattering 2018 Memorial Day tweets. They exceed even the heartless comment in a speech to Congress—in the presence of a grieving widow—that a fallen Navy Seal would be happy that his ovation from Congress had lasted longer than anybody else’s.
It’s not news that there is something missing from Trump where normal human feelings should go. His devouring need for admiration from others is joined to an extreme, even pathological, inability to return any care or concern for those others. But Trump’s version of this disconnect comes most especially to the fore at times of national ritual.