All politicians are, by definition, corrupt.
The few that seem to be honest, don't make it too far. Carson, Sanders, Cruz. (I know this is a GOP thread, by I think Sanders is pretty honest, though WAAAYYYY off with his policies).
The only form of government that has the potential, though no guarantee whatsoever, to be honest, is a מלך מבית דוד, and that's just because they were chosen. They still have (and had) בחירה חפשית to do wrong, as we see in נ"ך. But since they were chosen, the G-d given potential does exist for them to be honest, unlike any other form of government that was not chosen by the אויבערשטער.