They can't do whatever they want. They can do more than you'd want them to be able to do, but they can't just take billions of dollars and put them in their own pockets. Company bribes makes every American politician a multi millionaire, sure, but if they could do what they wanted they would be multi billionaires like the rulers of Russia and China.
It is also susceptible to "don't let the other guy win!" type of propaganda, especially in FPTP electoral systems like the American one. So long as you can find enough emotional wedge issues to ensure that your base will never even contemplate voting for "the other", you can basically do whatever the hell you want.