It's not an exemption, it is an immunity. It is a little used and almost archaic clause of the U.S. Constitution called privilege from arrest for Senators and representatives. It doesn't apply to civil or criminal process, but civil arrest. What TSA is doing is a process. We did the same thing in Customs. Civil process, no arrest. Also the immunity did not apply for treason, felony or breach of the peace. https://constitution.congress.gov/browse/essay/artI-S6-C1-1-2/ALDE_00001047/TSA doesn't recognize this as an exemption in their CIVIL penalty framework.
Encountered any number of Senators and Representatives during my career. Hands off as they were always traveling to or from Congress. Their aides sometimes had issues, those we could deal with.