Market manipulation. If you can tank the stock market at a time YOU know well in advance, then you stand to profit "tremendously".
He or people in his stead might have purchased put options ahead of the anouncement of tariffs. -> profits When he then says "it was just a prank brooo!" he can make money by buying the now devalued assets and sell them as soon as they recover. rinse repeat.
I smell market manipulation maybe I am mistaken this smell and it is really the smell of mental instability....
Maybe he's been told Melania is ukranian....