It's simple: In wartime you monitor the enemy's communications.
Of course, we've got plenty of ops around the world doing this 24/7 and have been for decades.
This issue is about mining domestic communications, which is an infringment.
It it is argued that the only "wiretaps" being done are international phone calls to known "persons of interest" then that is indeed cause and a warrent would be in order for DOMESTIC communications.
No...it isn't. It's about mining foreign calls, including those that come to people in the United States.