That's not how border security works. They don't need a warrant. The courts have decided this.
There was nothing illegal that happened here.
Even if you're a returning US citizen?
This word "freedom". I don't think you (or most of the USA) knows what it means even though you spend your entire lives repeating it.
Yes, even if you are a US citizen and yes, the "border" means up to 100km from actual border.