Trump loves to proclaim that something or someone is "sad." And like the man he used to mock (Jeb!), Trump loves a good exclamation point.
"Sad!" works as a synonym for "pathetic", and not as a description of actual tragedy. Donald Trump is fond of labeling people he does not agree with as being "sad!"
Affection for this term has spread beyond Trump diehards, and made its way into the vocabulary of the political pundit class, as well.