I think he literally forgot every memory, so that when he's standing there in his office he thinks, "Who am I? Where am I? Who is this dead woman on the floor?! Why is there a GIANT FLAMING PLANET in the sky?!! OMG, why is my body made of spare parts?" and then he decides to become president. As you do.

Probably he remembers basic skills like speaking and driving hot sports cars and how to do his taxes...