I have heard these concerns expressed by others. I think, however, that not all people pose the same risks.

Temperament or other personalities disorders make this even more risky when considering the Presidency.

For example, a President whose approach is to listen to people and who has trusted support/advisors (while not optimal) would not pose a global risk. He may struggle with decisions but is less likely to make extremely bad, reckless decisions.

But a President who thinks that he and he alone has all the answers, who has not developed close trusted relationships and who has among his advisors "yes" men, could pose huge global risk as he could do just about anything and there would be no guard rails.