What I feel like people do here is map everyday abusive law enforcement behavior onto that border search exemption without realizing that what they're actually suggesting is that people should expect (and thus roll with) a "tear everything apart, search under clothes, maximally invasive" border search, which is what the Constitution authorizes at an actual border crossing.
Technically, the entire fourth amendment applies. BUT All the fourth amendment requires is probable cause for warrants, and that searches and seizures be reasonable. It doesn't require warrants for searches or seizures (although courts have found that that is usually necessary for reasonableness), and it doesn't require probable cause for searches or seizures without a warrant (though courts have found that that also is usually necessary for reasonableness.)
What the courts have allowed is the use of the border zone to justify exceptions to a lot of the things that are usually required for reasonableness. This isn't, technically, an exception to the Fourth Amendment, because searches still need to be "reasonable". Its just proximity to the border makes searches "reasonable" that wouldn't be anywhere else.
I'm doing ["border search" "miles" site:uscourts.gov], getting cases --- recent cases, including some with cites to Ameida-Sanchez, which of course makes my point --- and not seeing much to suggest that CBP can randomly search random cars in Green Bay WI under the border search exemption.
And now here we are with most of the population of the USA without rights and the president able to declare anyone left a terrorist and use the military against them.
(1*: https://en.wikipedia.org/wiki/Killing_of_Abdulrahman_al-Awla... )