I'm sure smart people have already made this argument

This occurred to me while I was driving the other day - part of the reason we have trouble with politicians being bought is because making donations to a political party/person/cause/whatever is considered a form of free speech, right?

Two things here: 1) it's called FREE speech.
2) the entire concept of free speech (as I understand anyway) is that any and everybody has the right to speak as much as they desire about anything they desire. (With the obvious caveat of not shouting Fire in a crowded theatre, of course.)

By that very definition then, donation of money should not be considered free speech because not everyone has an equal amount of money to spend, so not everyone has the opportunity to "speak" as much as they want.