I would expect that the highest office in the land. Should be occupied by a person that is mentally competent. If there was any hint of a candidate was suffering from the early symptoms of Dementia. Would it not be important that these candidates be tested for their cognition. Given that over 150 other countries in the world will be affected to some degree, by Presidential decrees.
The modern world is immensely complex now, stressful, demanding. Surely, a President would need to be, way above, fit for the job?