Yeah, but...all the Presidential Libraries sell this kind of stuff.
My favorite from the Nixon library (sent to me by my daughter) is a tee shirt with a picture of Nixon greeting Elvis. It says: "The President Meets the King".
Yeah, it's not the chachka part. It's the self-aggrandizing part.
The Nixon tee that you cite ("The President Meets the King") is actually quite the opposite. It's self-effacing.