Miranda v. Arizona, 384 U.S. 436 (1966), requires that law enforcement officers read certain warnings to suspects before subjecting them to custodial interrogation. Failure to do so renders the defendant's statements elicited thereby inadmissible in court. One of the key factors in determining whether Miranda applies to a particular situation is whether that situation is "custodial." The standard for whether a situation is "custodial" is basically this: if the person is not free to leave, the situation is custodial.
In this article, A regional TSA spokesperson out of Miami is quoted as saying that "once a person submits to the screening process, they can not just decide to leave that process."
I contend therefore that the TSA screening process is now admittedly custodial, and that Miranda may now apply to all questions asked of passengers by TSA agents at airport security. Of course, travelers should probably not rely on that and make potentially incriminating statements to TSA agents, whether they've been Mirandized or not. I doubt TSA will be Mirandizing people.
Practically, the above-quoted statement is definitely evidence that the TSA process is becoming more and more adversarial. It is not merely infringing of passenger's rights--it threatens future violations as well. I know that if I am ever called upon to fly (and the circumstances would have to be dire to get me on a plane), I will not be answering TSA questions. Instead I will be unambiguously invoking my right to not make a statement and to have an attorney present during any further questioning.