If the Constitution says something, it applies to everyone everywhere. The Constitution of the United States does not apply to people it applies to the government. It says nothing about "US citizens" or "foreign nationals". It restricts what the government can do.
So if the fourth amendment right to protection against unreasonable searches applies here (which there seems to be some debate about), it would apply to everyone. Not just to US citizens. The government does not have the right to perform searches of personal property without a warrant detailing exactly what will be searched. Again, this restriction applies to the government, it is not a protection afforded to citizens.
My understanding has it that in practice "the people" means roughly "all citizens and residents of the US", not all people anywhere. You can disagree with the courts over what the words mean, but do so deliberately.
That is an excellent article! I actually learned quite a bit from that, thank you.
The main take-away that I had is that the courts generally uphold "the people" to mean "citizens", but there are some strong divisions on that and the case is far from settled. At the very least I agree with Harvard's opinion that this judgement cannot hold true to all instances of the the phrase "the people" without massively undoing hundreds of years of case law.
Based on that I will change my statement here to say "the Constitution restricts the government, but it's unclear in the courts whether it restricts the government's actions against non-citizens, although it probably should according to constitutional law scholars". So if you're a tourist in the US, watch what you say and do, because you may not have any right to freedom of speech or protection from unreasonable search and seizure.
Interestingly, the german preliminary constituion (we don't have a real one) that was written by the WWII allies also is about people but unambigously means all people on earth.
'Article 1 of the Basic Law (in German legal shorthand GG, for Grundgesetz), which establishes this principle that "human dignity is inviolable" and that human rights are directly applicable law, ...'
To be honest, I've not given the article I linked a careful read.
My understanding is that it's entirely uncontroversial (as a question of "is" rather than "ought") that those who are neither US citizens nor US residents, while also not present in the US, are not afforded the protections in the Constitution given to "the people". It is also entirely uncontroversial that they do apply (in sometimes disputed form) to American citizens in the US (and probably also while abroad), and that they usually apply to long-term US legal residents present in the US. Some other points on those spectra are less certain (especially to me).
The question is not whether foreigners are people, but whether they are a part of "the people", usually taken to mean "the people of the United States" - which is the context in which "the people" first appears.
The Constitution is American law, and American law does not apply extraterritorially except in narrow cases. That's a bedrock principle of Constitutional law. The only thing that binds the US government abroad is the law of the jungle.
And yes, I know, human rights and international law are kind of lacking enforcement, so compared to stealing a lollipop or something, of course there is no legal problem with what the NSA is doing. But "it's gotta be okay or it wouldn't happen"? Nah.
Citizens of other countries in fact don't have the same rights and protections against the NSA as citizens. It's why the NSA exists.