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.
Everyone shares lists.
I have a politics label in gmail that is blue/red from 2012 onwards. All the GOP emails are from poking around Romney 2012, and nothing else.
I'd say you'd be surprised on the reuse, but you shouldn't be.
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 "[email protected]".