But once he was aware they were seeking evidence, his giving the duress code was "destroying evidence", which is clearly a crime.

Let's go down a hypothetical rabbit hole: It would only be "destroying evidence" if there was evidence of a crime on the phone. What if the guy blanked the phone, because he didn't want the Gestapo poking through his personal e-mails and texts, on principle, even though there was nothing illegal about his correspondence? If there is no "evidence", how do you prosecute for "destroying evidence"? Or are we so far down the trend, that we now need to prove our innocence?

Second hypothetical, what if the guy blanked the phone, before he got to the US, because he didn't want the Gestapo sifting through it, even though he had not been notified by the Gestapo they wanted to sift through it?

Keep in mind the thrust of the programs FEMA wants to fund, programs designed to detect "pre-crime". We do seem to be edging toward assuming everyone is trying to hide something, and everyone needing to prove their innocence. Saw an interesting cartoon on FB yesterday. One guy saying "I'm fine with mass surveillance, because I'm not doing anything wrong". The other person says "...until someone changes the definition of what is "wrong"".

Steve