You may not search someone without a warrant whose only motive is to enter into the public domain!
What a great way to put the last nail into Amtrak’s coffin!
Wrong. The legality of a search is not based on the motive of the person being searched.
If LE/HS agents had legally appropriate information that made a search of deboarding passengers appropriate, the search is legal. That is all.
You want to put a nail in Amtrak's coffin, let a terrorist attack go down, either on a train or by a passenger using the train to transport either himself or his weapons.