One thing is sure ... WE WON'T SOLVE IT HERE! "It," being a query within a Comment on my Nelson post. Upon reading my post, our colleague was moved to say that surely such leadership traits are born ... and that's that.
On this eternal issue, I've come down on the "born" (more accurately, born or bred early) side more than the "trained" side more than most of my colleagues—no surprise since many of them are leadership trainers!
Intelligence, dispositions such as energy and enthusiasm, and the likes of a proclivity for hard word work are pretty well set in something like stone before we "employers" get our mitts on a person.
Consider: I worked briefly with a speaking coach decades ago. He declared me a "pleasure" to work with. I remember him saying, "Tom, it's a lot easier to work with someone energetic—and try to help them round off the rough edges—than it is to try and 'spice up' a turnip."
I think that personal vignette is very near the heart of the matter. There is—clearly!—some stuff that one can help with. I had a colleague, a fine and caring person, who never took the time to send "Thank you" notes or perform other overt acts of recognition. (My assessment: He had been raised in a very reserved setting, and one mostly kept one's emotions to oneself.) Now if this person had been a misanthrope, I wouldn't have bothered. But that not being the case, I banged on him for a period of years—and today he surpasses me in this vital area of human interaction.
There are a lot of things, then, that can be brought to life, or things that have worked for others that one can be made aware of. I've observed—back to Nelson—that a lot of high-powered leaders, up to and including U.S. Presidents, devour good biographies and autobiographies. Read enough, a few hundred I should think, and one sees some commonalities in the way certain types of situations are handled—e.g., building support for unpopular causes, such as Roosevelt's efforts to convince a skeptical Congress of the wisdom of going to England's aid in WW II.
Bottom line: Train "fundamental dispositions"? Tough! Provide a bushel of useful strategies for working with people and situations? Yup!
To allow myself to lean a little to the "trained" side, I admit that I am trained in part as a Rat Psychologist. (No, alas, I didn't inspire Spencer to write Who Moved My Cheese.) Thence I believe in the primacy of repeated positive reinforcement—even when dispositions are at issue. Get a person hooked on Toastmasters, for instance, and after she or he has declaimed in public 50 times, the "Inherent" Fear of Public Speaking will indeed wane, even if one does not become the next Reagan.