...is a Passport Card -- basically a secure national ID issued by the Department of State ($45 new, $35 renew for non-passport holders, $20 for passport holders, lasts 10 years). Over a million Americans, including myself, carry one -- that's more than the population of the Omaha metro area. It's for car, train, bus, and boat travel within North America, but can also be used as a single identification for getting a job (along with, if I recall, the standard ICAO-compliant passport and the green card), and is recognized by the TSA (for domestic air travel), liquor store, and just about anyone else who needs ID. The RFID chip just has a database pointer, which differs from the card number if memory serves, but it comes with a tin foil hat just in case.
What this idea amounts to is transferring or cloning the passport card program into Social Security or Homeland Security.