In favor of the "power just allows corrupt behavior" theory, Bueno de Mesquita offers two very nice examples of people who ruled two different states. One is Leopold of Belgium, who simultaneously ruled Belgium and the Congo. The other is Chiang Kai-shek, who sequentially ruled China and Taiwan, allegedly rather differently. (I heard him speak about these examples in this podcast. BdM, Morrow, Silverson, and Smith wrote about Leopold here, gated)