My previous posting on the Proud Boys spam email speculated that voter records were widely available for such purposes. Here’s a story from 2017 reporting that voter data for about 198 million Americans was spilled from a “storage bucket” on Amazon’s Simple Storage Service (S3). The story shines a light on “big data” in elections and data brokers who provide such data to political organizations.
Regarding Amazon and the storage spill, these incidents are generally blamed on the data owner (Deep Root Analytics) for failing to properly protect their data. It’s worth noting that Amazon serves thousands of such unprotected buckets.