Actblue requires a phone number and email address.
As far as I know, physically mailing a check is the best way to avoid sharing information as you only need to provide your name, address, and employer. This information is the only federally required information.
I don’t know. What’s weird is that I think it is up to the campaign to make sure they have valid contact information. So I suppose there is a risk that the campaign might get dinged?
