It's also reasonable for CBP agents to be able to enforce border-related laws anywhere near the border, subject to the usual law enforcement requirements of reasonable suspicion of a crime based on objective evidence for brief detention, and probable cause for any kind of search.
What I find unreasonable is any kind of checkpoint where a substantial number of people passing the point are unlikely to have crossed a border. For example, there's a permanent checkpoint on I10 about 15 miles west of Las Cruces, NM. It's over 30 miles from the border with Mexico in a straight line, and much farther by road. Most people passing this point are traveling between two locations in the US. Everyone is stopped and questioned, and while the questioning is usually not very invasive, it's done with zero individualized suspicion.
I’m not saying that’s a good place for a border check station. I’ve always thought it was silly, but it’s been there for a while.
This whole "well, they need some space around the border to operate" seems to be a red herring. No one's objecting CBP from setting up checkpoint buildings at the US border. They've been doing that since 1789. The extension of this space to 100miles is a travesty. Make it 0.5Mi so CBP can't waltz around random bus stations, and no one will complain.
[1] https://www.wweek.com/news/courts/2019/01/28/border-patrol-c...