Clearly, it didn't apply to Ronald Reagan, whose Economics training and his deep love and reading of the writings of America's Founders made him far superior in his understanding of the challenges of the Cold War era and how to deal with them. His handwritten letters and notes, as well as his own thoughts in his speeches reveal a far deeper intellectual ability than his critics would have had us believe.
Even the attempts at discrediting Dan Quayle were pathetic and reveal much more of the failed and failing ideas of the Left than they did of the qualifications of Quayle, whose conservative ideas were the Left's real target, not his mental qualifications.
If one wanted a quick check and comparison of the intellect and decision-making ability of George Bush vs. John Kerry, one had to look no further than the first choice each made for a Vice President for these United States. Really now! What did the millionaire personal injury lawyer from NC bring to the job except ambition and pompous rhetoric?
By the way, in this post-9-11 world, have you ever heard anyone (Right or Left) say: "I'm just so sorry that Al Gore is not our President"? Didn't think so!!
In reality, he had far deeper intellect and ability than any of his critics, particularly the obnoxious among them. Those who could comprehend his strength never tossed around the "affable dunce" slander about him. They kept their difference "professional" not personal.
The cool thing about RR was that he was so comfortable in his abilities, that the small minded critics never phased him in the least. He never felt the need to respond in kind to their venom. I see many of the same qualities in W.