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Here's a relevant passage from FindLaw.

First they talk about actual border stops (all emphasis mine):

Border Searches .--''That searches made at the border, pursuant to the longstanding right of the sovereign to protect itself by stopping and examining persons and property crossing into this country, are reasonable simply by virtue of the fact that they occur at the border, should, by now, require no extended demonstration.'' 87 Authorized by the First Congress, 88 the customs search in these circumstances requires no warrant, no probable cause, not even the showing of some degree of suspicion that accompanies even investigatory stops. 89 Moreover, while prolonged detention of travelers beyond the routine customs search and inspection must be justified by the Terry standard of reasonable suspicion having a particularized and objective basis, 90 Terry protections as to the length and intrusiveness of the search do not apply. 91

Then they talk about inland stops, broken down by roving patrols vs. fixed checkpoints.

Inland stoppings and searches in areas away from the borders are a different matter altogether. Thus, in Almeida-Sanchez v. United States, 92 the Court held that a warrantless stop and search of defendant's automobile on a highway some 20 miles from the border by a roving patrol lacking probable cause to believe that the vehicle contained illegal aliens violated the Fourth Amendment. Similarly, the Court invalidated an automobile search at a fixed checkpoint well removed from the border; while agreeing that a fixed checkpoint probably gave motorists less cause for alarm than did roving patrols, the Court nonetheless held that the invasion of privacy entailed in a search was just as intrusive and must be justified by a showing of probable cause or consent. 93 On the other hand, when motorists are briefly stopped, not for purposes of a search but in order that officers may inquire into their residence status, either by asking a few questions or by checking papers, different results are achieved, so long as the stops are not truly random. Roving patrols may stop vehicles for purposes of a brief inquiry, provided officers are ''aware of specific articulable facts, together with rational inferences from those facts, that reasonably warrant suspicion'' that an automobile contains illegal aliens; in such a case the interference with Fourth Amendment rights is ''modest'' and the law enforcement interests served are significant. 94 Fixed checkpoints provide additional safeguards; here officers may halt all vehicles briefly in order to question occupants even in the absence of any reasonable suspicion that the particular vehicle contains illegal aliens. 95

So, it's not that you don't have any 4th Amendment rights at the border, but that the 4th Amendment's requirements for "reasonableness" of the search are met by virtue of you coming into the country. This is why you will meet Customs & Border Protection officers if you were to fly into any international airport, regardless of how far it is to a "border," like Denver, Atlanta, or Salt Lake City. It's still a port of entry into the US.

Landmark case supporting this Border Patrol action:

US Supreme Court, Decided July 6, 1976:
UNITED STATES v. MARTINEZ-FUERTE, 428 U.S. 543 (1976)

1. The Border Patrol's routine stopping of a vehicle at a permanent checkpoint located on a major highway away from the Mexican border for brief questioning of the vehicle's occupants is consistent with the Fourth Amendment, and the stops and questioning may be made at reasonably located checkpoints in the absence of any individualized suspicion that the particular vehicle contains illegal aliens. Pp. 556-564 ...

HOWEVER, that does NOT mean it is RIGHT! IMO, some tell-tale indications of this (i.e., that the SCOTUS is turning a blind eye to the 4th Amendment) is WITHIN this SCOTUS Opinion:

There also was a grave danger that such unreviewable discretion would be abused by some officers in the field.
As we have noted earlier, one's expectation of privacy in an automobile and of freedom in its operation are significantly different from the traditional expectation of privacy and freedom in one's residence. [and if I pull up to a Checkpoint in my RV that I'm living out of, what then?]
It is agreed that checkpoint stops are "seizures" within the meaning of the Fourth Amendment.
In summary, we hold that stops for brief questioning [note: "stops," NOT search and seizure] routinely conducted at permanent checkpoints are consistent with the Fourth Amendment and need not be authorized by warrant.

WHY did the Framers give YOU and I protections under the Fourth Amendment? How has it "evolved" since their dealings with the British vs the problems we face in 2009?

Psst ... the Colonists had to deal with terrorism, illegal immigration, disease control and contraband, too!

Police have the right to reel in wrongdoers BUT not to go on fishing expeditions.

If you are willing to give up your Rights, then you are subject to (AND deserving of) whatever new Law or Judicial ruling that ANY public official is willing to "modify" from the Bill of Rights -- all in the name of the "public good".