I'm unable to find and get into the TOA. whatever that is, referred to here, on the Net, and don't have a current dictionary of acronyms, so I may be missing something. This problem appears to be with a local transit authority police agency and Delta Air, not federal TSA, though the shirt, whatever it said which I don't know, did question. challenge, or attack TSA.
I don't hold with racial, ethnic, religious, etc. discrimination, official or by public accommodations like airlines and restaurants, and they cannot justify that by claiming that customers might be biased against the person, either, but of course there is no law against excluding Ph.D. candidates because everybody knows, especially since "9/11" and the Aurora CO theater shooting, that some of those might be studying something dangerous like those. (For the record, I have only one earned doctorate myself, a J.D., the basic law degree). I've read about two successive directives by TSA's parent Homeland Security Department listing practicing Christians, believers in upholding and defending the Constitution, and the Second Amendment, part of the Bill of Rights thereto, veterans and special forces trainees, etc. as suspiciously likely to commit assassination, terrorism, etc.
I have a congenital nystagmus condition, which, under Texas and many other jurisdictions; law, is probable cause for a warrantless arrest, breath or blood test, and search because the same symptoms, uncontrollable eye movements, etc., can be produced by alcohol or cocaine. I also have poor vision and eye-hand coordination, no depth perception, etc. as a result of this and other congenital neurological anomalies. I have been detained, and got pulled out and screened, not when boarding but after landing at my home city one night because I was visibly upset after a federal functionary had me fly to New Orleans and then they asked me why I came and said the problem could have been solved on the phone, so my involuntary eye movements wee more pronounced than usual--and that was before TSA. It took 24 years before the CIA finally quit lying to my U. S. Senator and me and admitted to me that they had put and kept me on a list of suspected Soviet spies and sympathizers, not only false but easily proven false, over a piece of academic research. I still can't get TSA to tell me if my nystagmus condition etc. and my mostly conservative political views, openly published, has me on a "no fly" or "suspicious" list. Nobody will tell me how to vote or board a plane shortly after my wallet with my state non-driver ID card (which it took me 14 years to get Texas to issue and then to integrate into the main drivers' license system) was lost or stolen, either.
I know of no airline or TSA rule that might provide any even remotely legally arguable legal basis for denying a passenger carriage on a plane because of any political message, unless it was grossly obscene, indecent, etc.,not revealed here, in which case turn the shirt inside out for the flight. "Delta commits Unfair Labor Practices" would be protected, especially during a strike or lead-up job action.
If the pilot had bumped these people to avoid delaying takeoff, pilots do have broad discretion, but it they had been allowed to board and had boarded before being kicked off, that doesn't make sense on the information given to date.
Obviously something ticked the state Authority that runs the airport and its police.off. State and federal civil rights authorities should investigate what, if any,Constitutional and other legal rights may have been violated. Winning a civil suit might be very hard regardless of many possible facts.