Except travelers are not "on us soil" until granted entry by customs. Customs could just deny entry if foreign travelers won't voluntarily consent to search.
The last time I so much as questioned an american customs agent about something they asked me to do, I was interrogated for 2 hours about my life, job, friends, family, phone searched, car flipped through, etc.
They even had 2 canine units circle my car and jump in and out of it at least 10 times each.
Some people get off on power, and this job is as close to having power over people as some can get.
As long as you know you're not actually carrying contraband or is a terrorist, just smile, comply when reasonable, and then say politely that you'd like to see their manager to file a complaint.
I travel across the US Canada land border from time to time (in the mountain west). My experience has been that Canadian officials are universally civil and respectful while US officials are universally not.
As a frequent traveler between the US and Canada, I’ve only ever got grief (including accusations of smuggling) from Canadian officials. Going to the Us side it’s usually a simple “have a nice day”.
It depends on the entry point. If I go through US customs in the Toronto airport, it's on Canadian soil. If someone there is having an issue with the process, they can withdraw their entry request and leave. That's perfectly fine and they shouldn't be punished for it. You don't have that option if you use a land crossing as you're physically inside the US.
Many US airports, especially away from the coasts, don't have any immigration/customs facilities, instead flights from Canada to the US go thru US customs in Canada (make sure you get to that flight early) since it's cheaper to put US facilities in a relatively smaller number of Canadian Airports
I recommend caution when asking the agents at Shannon if the Republic of Ireland still has sovereignty from the United States of America. In my experience, it hits a nerve.
The Bahamas also has US customs there. You do the immigration part before boarding your plane. And you land on the US on a domestic terminal and don’t go over customs.
But customers officers can't force you to comply can they? So whether or not they have any authority is irrelevant. Of course if you choose not comply you have to turn around.
Sure... but I don't know where US citizens will go if they do not have residence in another country. Not everyone getting searched reside outside the US.
In that case you as a citizen are allowed to enter, but whatever they're searching (phone, computer, etc) may be detained and you'll be given a receipt and (often) an opportunity to claim it at a later date.