Tomorrow's?

I suppose when you say "needs", you are making some argument that the constitution requires some minimal level of respect towards US citizens; however, a more expansive definition which includes moral imperatives would require that American law enforcement follows the "general principles of law as recognised by civilized nations"[0] as well as "international custom"[1] at least as regards international actions.

Even from the perspective of its own constitution, though, America is bound by its commitments to various international civil rights treaties that it has ratified, such as the ICCPR, which requires it to "protect and preserve basic human rights such as the right to ... privacy"[2].

Of course, countries do generally spy on each other's citizens, so it's difficult to say what it would take to breach international law (even assuming there were a court that could exercise jurisdiction over the issue), much less what it would take to trigger a constitutional challenge in US domestic courts over such a breach, but if, for example, the CIA started deliberately publishing every foreign citizen's private emails, just for the lolz, I would hope that even allies would declare this a breach of international law.

[0] https://unimelb.libguides.com/internationallaw/sources#s-lg-...

[1] https://unimelb.libguides.com/internationallaw/sources#s-lg-...

[2] https://civilrights.org/edfund/resource/where-the-united-sta...