I hope he doesn't just let this go. He needs to talk to a lawyer. And then the media. The thugs who did this to him, all of them, need to be made to suffer. At least public humiliation via name and shame, preferably financial harm though that is extremely unlikely. But name and shame would do it. If the DHS and FBI and TSA folks wives and kids were spit on in public for being related to such scum, the DHS, FBI, and TSA folks would reconsider their profession and their professional behavior.
Personally I think he should have refused to continue answering questions until he was given water, or just outright start refusing to answer questions, but i wasn't there.