Originally Posted by Wally Bird

Far too simple an 'answer'.

A Federal LEO may demand ID on federal property (which includes federally-controlled areas such as customs halls etc.). Otherwise there is no Federal statute requiring anyone anywhere else to identify themselves on demand.

There are, however, individual state laws. Nevada for example has a stop-and-identify statute but even that requires only that you identify yourself verbally; it does not require you to produce proof. But of course you will likely be detained until you do so, and the police will have no qualms about the legality of such a detention.

Read the Hiibel case for further instruction: http://supct.law.cornell.edu/supct/html/03-5554.ZS.html , although unless you are also prepared to mount a court challenge, the practical answer in airports is yes, show the ***** your ID otherwise you will miss your flight.

Sad, and only going to get sadder