And, based on the inscription, it might even be a practical joke autograph, played on the recipient by a friend. Seriously, would the disgraced former president write "Good luck in your position as a politician" ??? It made me chuckle.
The idea that this might be a practical joke might be an answer. A book signed by Nixon is not a rare nor expensive item, so why bother creating a forgery? Still, overall it’s not a bad representation of Nixon’s signature, apart from the way he starts it.