https://en.m.wikipedia.org/wiki/United_States_Border_Patrol_...
If you check this in the search bar at the bottom of the page you'll see this has come up a bunch on HN (it's a lurid and exciting notion to toss around!) and there are SCOTUS cites in the results.
It is not my contention that CBP isn't abusing the law. I'm sure they are. Many CBP immigration stops apprehend no or single-digit unlawful immigrants while arresting dozens and dozens of citizens for things like suspected drug offenses. My contention --- well, not really mine so much as that of the Supreme Court and of law review articles about this case law --- is that what they're doing is plainly unlawful.
What is plainly the case is that many people believe that the law dictates that CBP can warrantlessly search citizens anywhere within 100 miles of the border (that border including the shores of all the Great Lakes). The law does not say that, the Supreme Court has repeatedly said that CBP can't do that, and people should stop repeating the claim that they can, because that claim empowers the CBP, which is already prone to abusing its authority.
But the bogus claim is head-turning, and presumably generates a lot of money for ACLU, because it's alarming and wrong-seeming (well, wrong, period, but...).
"The Immigration and Nationality Act of 1952 established that a "reasonable distance" of the border would extend "100-air miles" around the outline of the country. "
Update: addl reference [3]
[1] https://www.snopes.com/news/2022/06/13/what-is-usa-border-en...
[2] https://tile.loc.gov/storage-services/service/ll/fedreg/fr02...
[3] https://ballsandstrikes.org/legal-culture/border-patrol-100-...
"This longstanding recognition that searches at our borders without probable cause and without a warrant are nonetheless "reasonable" has a history as old as the Fourth Amendment itself."