“The NSA has a duty to keep an eye on foreign interests who plot against us.”
The NSA think that they have a duty to keep an eye on all who might plot against us.
“We can’t prevent attacks on the homeland if we don’t know about them.”
That is why they are keeping an eye on everything, not just foreign activities.
“That duty does not outweigh the constitutional rights of American citizens.”
This is what I meant by shit and carpet analogy.
They do ... if by "all" they mean those who aren't American citizens residing on U.S. soil.