I don't think it's a problem of defining ever more detailed or different government rule sets, but a problem of the feedback between the people governed and the people governing. The institutions of law provide some help - mostly by beneficially slowing down how fast things can change, but the maintenance of a stable government is a balance of politicians and leaders do, and what people allow. A much more dynamic, and fragile relationship than most of us care to contemplate.

There are more than "politician corrupted by power" stories, there are also many politician does a good thing and fades into the background, or politician leads well for a long time stories too. These are less exciting and usually receive far less press, because they are remarkable in their unremarkable outcomes.