It was likely written by his staff, but I will say that, if that Trump had been around the last four years, he wouldn't be giving a farewell speech today.
You realize "that Trump" literally doesn't exist, right?
Yes, I realize that isn't his natural state. He's acted similarly to that a few times before (such as a couple of his SOTU speeches), when he just lets his aides talk through his mouth, so to speak. I know it's unreasonable to think he ever could have kept that up, but I do think he would have won re-election if he somehow had.
