It's clear to me that President Trump wanted his official photo to be a "reshoot" of his historic mug shot albeit with a few improvements in lighting and perhaps pose. But don't take my word for it. "The Body Language Guy," Jesus Enrique Rosas, covers it all in detail
here.
(I've been following Rojas on YouTube for a while. He's definitely on our team (I bet you hear lurks on this thread) and he's very funny.)
His expression says to me "I know what you did...and I'm coming for ya!"