This is actually pretty clever on the part of the NSA.
NSA procedures prevent NSA employees from investigating US persons in most cases if communications are entirely within the US. That way most NSA employees can feel like they aren’t violating the inalienable rights of their countrymen. However, if all data are sent to Israel, their signals people can process the data and investigate triggered communications.
Sure, the source document cited by the Guardian article stipulates that 4th Amendment guarantees are to be upheld. And, if you believe that interpretation corresponds to the plain meaning of the words of the 4th Amendment, well, think again. And, if you believe Israeli intelligence services cares about any interpretation of the 4th Amendment, you’re hopeless.
I recall a story that came out years ago that alleged the UK and the US listen in on the other nation’s phone calls, then simply exchange the info.
Freegards