If tomorrow I owned 1 zillion dollar, that wouldn't make me able to change the course of next US (presidential) elections. It's not the only factor, ofc, but it is a very relevant one. Let's consider other factors that might be relevant: influence, visibility, arguments, fame, political weight, political knowledge, time, will. There are others. Someone with no influence on these factors and no money can hardly influence the outcomes of a nation election. If that someone was made a billionaire overnight, it can gain control over some factors, improving the likelihood of their impact over the next elections. Will they succeed? Not necessarily, but that their impact can become perceivable is undeniable.

Fair elections: in the US there are a bunch of practices related to vote that I don't consider fair. First and foremost, how votes are counted. Then, how money can be used to finance parties and campaigns. Gerrymandering is another one.