Voter registration databases are available from the Secretary of States office in each state. Anyone can request a file dump; however, some states often charge a small fee for the file. GOP and NDP use different tech stacks, but both are tied to companies (like NGP) that have built processes around obtaining and updating voter registration data yearly from each state. They then tie in historic data they have from door to door canvassing, voter turn out, and any other touch points to build a profile about the voter. Typical data points include voting history, gender, various voter level flags indicating if the voter supports causes/activism, and any other notes or voter related data.