But he wouldn't be mentally fit.

If he decides to ride the spaceship as a passenger, he'll be confused, and somehow thinks he's the pilot. He'll be asking the stewardess every ten minutes where his spaceflight meal is despite being repeatedly told that they don't serve spaceflight meals. And if he sets up shop on Mars, it will probably be an ice cream parlor and soon (very, very) soon, he'll be asking where are all the milk cows he needs to make his ice cream.

On the other hand, maybe, in the here and now, he'd make quite the president on Mars, because at times, when I see him on TV, it seems like he's already there.