Economists don't talk about leadership too much, and sociologists seem to attribute leadership to the mystical magic of charisma. The only economic theory that comes to mind is Hayek's, which basically states that shit bags rise to the top because only shit bags would want to control other people. There's certainly some truth to that, but here I offer a more charitable view.
We choose our leaders based on the confidence they exude, since it's the best signal of expertise. No doubt this signal can be faked fairly easily for many people, but for the most part confidence comes with real expertise. And confidence is readily apparent. No need for credentials. The good news is that more and more people have access to the information necessary to create expertise, e.g. the internets. In other words, the world is moving towards a perfectly competitive market in information, where anyone can compete for expertise, and therefore leadership, in a given field. Thus, we have reason to believe that our leaders are better today than they were yesterday, and they'll continue to get better.
This is almost enough to get me interested in the presidential debates.