The Donald's Dangerous Brew

That is why, for me, experience edges out intellect as a presidential qualification. In the end, the smartest experts on substance, the canniest legislative tacticians, can and do disagree. The exquisitely difficult judgment calls that a president must make aren't simply a matter of being able to name international players in a journalistic pop quiz.

Rather, these moments call for leaders who have watched similar scenes play out so many times that, as with Bradley's rigorous practice regimen, they have developed an instinctive sense of where the ball is, and where it is likely to rebound.

This quality is what President Obama was referring to in his podcast interview with Marc Maron in June, when he talked about how he would be a better candidate, and president, an imaginary third time around. "I know what I'm doing, and I'm fearless," Obama observed. "And also part of that fearlessness is, because you've screwed up enough times, that you know that it's all happened. I've been through this."

Yet the primary ingredient -- and the fundamental attribute that disqualifies Trump from the presidency -- is temperament. This is a catchall that includes the capacity to lead and inspire; qualities of integrity and discipline; aspects of personality that range from steadiness to charm. To take the most vivid modern example, Richard Nixon's intelligence and experience could not compensate for his paranoia and dishonesty.

Trump's temperament issues are not Nixonian. They are distinctively Trumpian: his incessant need for self-aggrandizement, his reflexive intolerance for being disrespected. These form a dangerous brew in a potential president, equal parts narcissism and its mirror image, insecurity.

Donald Trump shouldn't be president, but it's not because he doesn't know the difference between Hezbollah and Hamas, or Quds and Kurds. It's because he isn't embarrassed by this ignorance, or at least pretends not to be.

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Ruth Marcus' email address is ruthmarcus@washpost.com.