I just received a letter from the Democratic National Committee.
The front of it stated in big letters - WE'RE SUING DONALD TRUMP I am a registered Republican so how did they get my name and address?
I did not open it but have written Return to Sender on both sides.
Corporations sell your data including your address. Allowing advertisers to build a profile on you. Which they then get contracted to send you shit.
Alternatively if an area has high registration for a certain party. Some State Parties just mass mail shit to every address in the zip code.