Fortunately, you can't typically "buy" elections by donating to campaigns.

Campaign spending does have an effect for unknown candidates, but once the voters know who you are and what you stand for, further spending doesn't move the needle.

It's true that the campaign with most money usually wins, but that does not the money caused the win!

One way to think about it is that the most popular candidate naturally gets the most donations, just like they get the most votes. It can also be a good investment to be on good terms with the future winner.