There's also the thing of picking your battles. There are changes one can and cannot make depending on the hostility of the political environment and if fickle potential voters have your back - which they have proven too often that they don't. There is also often sabotage in the delicate process of trying to pass and enact anything, sometimes all that is needed is one or two assholes from your own party to bring the whole house of cards down.

In an ideal world, they could try again, but for that we need educated and consistent voters to support them, and instead they get tarred with the label bOtH pArTiEs ArE tHe SaMe by the oh-so-pure crowd - "if I don't get everything in the first try I don't wanna try at all... not even one fucking day a year".
Meanwhile, the assholes on the other side send death threats to you and your colleagues. Their propaganda machine portraying you as a 'Murica-hatin' less-than-human caricature.

I cannot imagine trying to navigate this as a career.

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.