SC has a lot of deference to the Congress, and will go out of the way to find some convoluted legal language to justify something if it can be justified. So if the Congress and US public will be OK with mass surveillance, SC would not ride in on the white horse and save them from themselves. It would say "it's constitutional because of the precedent in 1834 that says blah blah blah and decision in 1928 that says foo bar bar foo, and you can't really expect privacy when you sending data out anyway, if you want it private, don't send it to nobody".