The power of the voter temporarily ends once the official is elected. As somebody said to me recently, "democracy can be like a sheep and two wolves voting on what's for dinner".
Perhaps the answer lies in nominating only good and trustworthy men, on both sides, and weeding out the garbage, like Bill Clinton, et al. But as Samual Adams said: "Our Constitution was designed only for a moral and religious people, it will work for no other".
OK, so why vote?
After all, your statement renders the voting process useless.
Again, I call out for a better system. I, personally, haven't found a better one.