I work with a small university psychology department, and one of our recently-retired faculty made a several-decade study of charisma, particularly among political leaders.
Her primary theory is that it is built out of a combination of formidable and approachable traits/behaviors. Naturally, there is a fair amount of personal variability in what we perceive as "formidable" and "approachable", so what seems charismatic will vary from person to person; it's not fully objective.
But her theory is that this is why you can have people who are, objectively, more repugnant still read as charismatic, and people who are very pleasant read as less charismatic: the latter may be very approachable, but they don't have enough formidability to synthesize that into charisma, while the former add just enough approachability that they can.
Her primary theory is that it is built out of a combination of formidable and approachable traits/behaviors. Naturally, there is a fair amount of personal variability in what we perceive as "formidable" and "approachable", so what seems charismatic will vary from person to person; it's not fully objective.
But her theory is that this is why you can have people who are, objectively, more repugnant still read as charismatic, and people who are very pleasant read as less charismatic: the latter may be very approachable, but they don't have enough formidability to synthesize that into charisma, while the former add just enough approachability that they can.