Joe Birkenstock was quoted in a Time article that examined how data and personal information is collected from presidential campaign supporters:
Typically, political campaigns gather donor information like names, mailing addresses, employers, and occupations, and sooner or later sell this information to other political groups. Less specific “metadata” can also be sold or “rented” to for-profit data brokers. Joe Birkenstock, former Chief Counsel of the Democratic National Committee and partner at D.C. law firm Sandler Reiff, says that such metadata can be extremely valuable, giving candidates indications about the state of mind of certain donors and the effectiveness of different speeches on contributions.
The rest of the article can be read here.