Your campaign donations are a matter of public record and Actblue harvests them and repackages them to sell to political campaigns and operatives. It's a shitty business model that preys upon an unfortunate part of federal law that most donors don't know about.
Your donation records to the fec are explicitly not allowed to be used for donors mining like this. I'm sure it still happens, but it's not the majority.
What happens is that the campaign you donate to to puts you on their list (allowed) and then shares that list with others in the party (also allowed). They share back and forth so fast you can't get out of it.
This is why it's the email that's shared not the name. FEC records don't have your email attached to to them, but the spam still follows unique emails like "candidate@customdomain.com".
It's not just the re-use and sharing of lists, but also the incredible Facebook-style targeting available to anyone for spamming. Anyone can sign up for something like ActionNetwork.org or NationBuilder and send out an email blast to registered voters in a particular zip code. NGP VAN is even more powerful.
The whole industry is mature and super targeted like any other spammer, but mostly immune to spam regulations (because politics are specifically exempt from CAN-SPAM etc., and most voter registration and donation data is public record). The whole pipeline is thoroughly automated and you're marketed and remarketed to just like you are with Google or Amazon, but without any of the already-minimal consumer and privacy protections.
Their targetting is shit. The people selling the targetting capability are scamming everybody else. I get countless spam messages from both political parties, both seemingly certain that I support them. I never donated to any of them.
If the price of living in a democratic society with transparent voter/donor records is a few annoying emails, we should all be paying that price gladly.
I dunno if that's either necessary or sufficient... in a country with legalized bribery, billionaire presidents, SuperPACs and all sorts of dark money, I doubt that knowing Joe Citizen donated $27 is really going to save democracy.
