That is patently false. Palin is about as "dumb" of a presidential candidate as you'll meet. Only one I can think of getting as much consideration as her would be Ronald Reagan, who was the ultimate puppet president.
Run down the list really quick. Needed a beauty pageant prize to get a scholarship to college. She took over 5 years and 5 different schools for her to get a bachelors in communication. That's not even a real degree. Now, I don't think she's truly dumb. I think she's average or slightly below average intelligence, but when you're playing in the world of presidential candidates where most everyone has a law degree or doctorate. Consider Dubya. He went to Yale, then Harvard to get an MBA. Maybe one of the "dumber" presidents we've had in recent year. Obama we all know and have been over ad nauseum. HW Bush graduated from Yale. Clinton went to Georgetown, Oxford, and Yale Law.
It's easy to call people dumb without considering the facts. Biden unlike Trump or Palin did get a law degree. Even if he coasted to it.