The population of Maine is about the size of Estonia. Why can't an individual state try to implement it? Surely that small scale is not a show-stopper.
OK... so at best you wind up with 50 independent state ID systems (although probably fewer, some states will absolutely refuse), none of which have any value outside their respective states (although more likely some do and some don't,) and no political will to integrate them into a single Federal system, out of unreasonable fears the US government will hunt down gun owners and put Christians into re-education camps, and more reasonable fears they might do those things to anyone else. Then what?
