Agree, the job is pretty merciless. People hate you whatever you do and even the most unsignificant of your mistake is used against you. If you became politician by idealism, you discover rapidly that persons involved makes you actually powerless: rival politicians, highly influencial ploutocrats, the supreme court (or equivalent), etc.

I have this impression with the US president. Despite the prestige of his position, he is actually highly powerless: most of the domains are in the hands of state governors, and if the supreme court, the senate and the house are not in his camp, he can barely do anything. It can be hard if you are really willing to apply what you promised but not being able to do so.