"The Central Intelligence Agency has a Medical and Psychological Assessment Cell. It employs or consults with doctors, sociologists, political scientists and cultural anthropologists to examine the conditions of top officials.
In the late fifties and early nineteen sixties, the CIA decided that they had expertise to look more carefully and in a more rigorous, analytical way at the health of foreign leaders in order to help give policy makers some forewarning of a transition in a government, stability of foreign governments, and also looking for potential points of diplomatic leverage.
The concern is not just the illness, it's also the medication that people take while they are ill and how that can compromise their decision-making ability, cognitively and intellectually. So they don’t make the same kind of decisions, their decisions may not be as predictable. They certainly may not be as, quote unquote, rational.
It can be decisively important because it can really change the stability of governments, particularly in authoritarian or totalitarian regimes, where there’s really a limited number of people who have powerful decision-making authority."