There's Supreme Court precedent establishing that this isn't the case. ACLU itself had backed off it, last I checked, but since they used it for a very long time in fundraising, people will never, ever stop believing that 80% of the United States lives in a "Constitution-free zone". You cannot in fact be border-searched on the streets of Chicago; in fact, you can't even be border-searched at a lawful fixed immigration checkpoint.
Border searches need a nexus to an actual border crossing.
The words of the law don't seem to matter much anymore. If the government does something, and they receive no push back (either from the people supposed to be checking-and-balancing, or from the victim in the form of successful lawsuits), then they, for all intents and purposes, can in practice do that thing.
> There's Supreme Court precedent establishing that this isn't the case.
This? https://en.wikipedia.org/wiki/United_States_v._Martinez-Fuer... or is there newer now?
> ACLU itself had backed off it, last I checked
They did, the current page greatly narrows the scope of their border-zone guidance to the SCOTUS case I linked before: https://www.aclu.org/know-your-rights/border-zone