Why Hillary Clinton Wants to Remember Your Birthday
Campaigns have several important sources of information about the electorate: publicly available voter data collected by states and counties, demographic data from the Census Bureau and other agencies, and data from businesses that can be used to build a richer profile of individuals. By asking supporters for their birthdays, the Clinton campaign can use that information to help connect individuals to those data sources. The value of this for large-scale campaigns is hard to overstate.