I know this is tangential to your main point, but in the US, you can only give a max of $3,500 to a candidate per election cycle, for each the primaries and general election.

To give more financial support, you have to do independent, uncoordinated campaigning for the candidate. So you can spend a million dollars on ads saying to vote for a candidate, but you can't give that money to the candidate's campaign and the candidate can't coordinate with you. This is what Super PACs do.

I only write this because a lot of people are unclear on the rules. I'm not making an argument about billionaires.