The 100-mile allowance

Why is it not unconstitutional?

In this 100-mile zone, Border Patrol agents have certain additional authorities. For instance, Border Patrol can operate immigration checkpoints.

  ACLU

Immigration checkpoints allow searches, don't they? I'm guessing a reasonable suspicion that premits the search is the color of a person's skin. Maybe not legally, but in practice?

The regulations establishing the 100-mile border zone were adopted by the U.S. Department of Justice in 1953—without any public comments or debate. At the time, there were fewer than 1,100 Border Patrol agents nationwide; today, there are over 21,000.

The Border Patrol often ignores this regulation and, aside from limiting interior checkpoint locations to within the 100-mile zone, rejects any geographic limitation on agents' authority. At least two federal circuit courts condone Border Patrol operations outside the 100-mile zone, federal regulations and Supreme Court precedent notwithstanding.

Federal border agents are stopping, interrogating, and searching Americans on an everyday basis with absolutely no suspicion of wrongdoing, and often in ways that our Constitution does not permit.

[...]

The ACLU believes that these checkpoints amount to dragnet, suspicionless stops that cannot be reconciled with Fourth Amendment protections.

  ACLU

I believe that also.

The expansion of government power both at and near the border is part of a trend toward expanding police and national security powers without regard to the effect of such expansion on our most fundamental and treasured Constitutional rights. The federal government's dragnet approach to law enforcement and national security is one that is increasingly turning us all into suspects. If Americans do not continue to challenge the expansion of federal power over the individual, we risk forfeiting the fundamental rights and freedoms that we inherited—including the right to simply go about our business free from government interference, harassment and abuse.

Aren't we there already? This might be closing the barn door after the horse has gone.