I had a friend who was traveling and was asked for a second ID at an airport, so he takes out his TWIC and the TSA guy says they don't accept them.
In order to get a Transportation Workers Identification Card, a document you need to get into ports to pick up freight, bulk loads of gasoline, and such you have to document your existence all the way back to Adam & Eve.. the amount of documentation is mind blowing. It makes the TSA background check for a Hazardous Materials endorsement on your CDL look like a hall pass.
So my buddy asked the guy why they don't accept one of the hardest documents in the country to get and the guy shrugs.