The current administration has stated that even for US Citizens, border entry suspends all constitutional rights. They've also said they believe this applies to allow warrantless searches within 100 miles of a border, which includes most major US cities, thus allowing ICE to search and kidnap basically anyone, not just immigrants. And they have stated that searching an electronic device is not a "search" as mentioned in the 4th Amendment and so you can't refuse to unlock the device or "destroy evidence". And that once you give them that access, that you have also "freely given" them access to your private social media, bank, etc., records and so those no longer require a warrant to access. And it's "gun to the head" tactics because they also believe they can detain you indefinitely in the 100 mile zone without a lawyer or any other usual rights, because you aren't being arrested, just an extended interview or whatever they call it. All in the name of terrorism prevention, of course.

Since they have corrupted the Supreme Court, this has been mostly upheld in various court cases so far. But any legal scholar will tell you it's nonsense. But that doesn't matter to authoritarians. They don't work within the law.

This has always been a well known rule.

Smartphones and the rules surrounding them at border searches are still pretty new, and they're likely enough to change. I think you might be overestimating the well-known-ness of these customs.

My understanding is that he is not the person who deleted the data, the agent did it by entering the pin. That’s an interesting wrinkle. Is that materially different than entering the wrong pin 10 times which often also wipes the device?

Yeah and it's even more stupid for him to be giving out interviews right now defending his actions. If I was him I would shut up in public and tell prosecutors that I was under extreme stress and pressure of the detainment and accidentally mixed up the real password with the duress password. The government can easily prove all elements for obstruction of justice "destruction or removal of property to prevent seizure" here, except for intent.

but you cannot delete your data

Said who?