Leo is the chief of staff - the equivalent of Andrew Card in Bush administration. Often the chief of staff will handle situations for the president which are less important, and on which the views of the president are already known. Josh is the Deputy Chief of Staff (he works for leo). This position currently belongs to Karl Rove in the Bush administration. Toby is the Director of Communications, which means that he's involved in speachwriting, as well as overseeing the other speachwriters.... most of these characters are people who you rarely hear about in real life, but are very important to the running of the administration (and make for interesting characters in a tv show). Overall, the positions and responsibilities held by characters in the West Wing are quite realistic, even if many of the events that take place seem far-fetched.

As for how people can call Bush Hitler when he has to run things by so many people: 1) he doesnt NEED to run things by any of these people. They work for him. 2) He picks the people who he runs things by (I'm not calling Bush Hitler, but Hitler also had high level officers who were heavily involved in decision making), and 3) many would argue that it's people like VP Cheney, or Karl Rove who really run things behind the scenes - though it is debatable how true this really is.