

It’s light exposure. The right side of the page is overexposed because it’s getting hit with (and reflecting, because it’s white) the majority of the direct light in the environment in which the photo was taken.
It likely wasn’t corrected because the focus of the actual image for the photographer was presumably Trump himself.
Here is an example of different types of exposure.
Uncontrolled diabetes (presumably type 2) might also at least partially explain his rapid cognitive decline. It’s systemic so it hits you everywhere.