But PRISM, as opposed to "upstream collection", isn't (necessarily) about searching foreigners abroad, or even at the border. It's about searching their stuff held on servers (sometimes) located inside the US and run by US companies as part of a business agreement with those foreigners. (However I have heard it suggested (IANAL) that sufficient legal cleverness can allow this to be characterised as a border search.)
> But it has never recognized a foreign intelligence exception to the warrant requirement when foreign-targeted searches result in the collection of vast stores of citizens’ communications.
Maybe. However the FISA appeals court certainly appears (IANAL) to have decided that a foreign-intelligence exception exists https://news.ycombinator.com/item?id=5917223 . Once again, from the Yahoo! case ruling http://www.fas.org/irp/agency/doj/fisa/fiscr082208.pdf :
2 . The Foreign Intelligence Exception . The recurrent theme permeating the petitioner's arguments is the notion that there is no foreign intelligence exception to the Fourth Amendment's Warrant Clause. 6 The FISC rejected this notion, positing that our decision in In re Sealed Case confirmed the existence of a foreign intelligence exception to the warrant requirement.
And again, this is a ruling on a law which allowed intentional targetting of US persons, though outside the United States.