i could be completely wrong here, but the concept of donating money to politicians or political parties seems to me (as a european) to be mainly an american thing.

though i guess even there it's probably a rather small percentage of the population that actually cares enough about individual candidates to donate money to them.

I don’t think it’s particularly uncommon in the US and the donation data is public. This is just the first thing I found on Google, Bernie Sanders had over 5 million individual contributions like halfway through his last campaign [0]. Not to mention that campaign donations can also be for local elections.

[0] https://time.com/5757711/bernie-sanders-34-million-q4-fundra...