At what point can the NSA and other intel units monitor our communications?

While I believe the intention behind your question is to raise the issue of whether it may and/or should be legal for government agencies to intercept domestic communications; I am not certain this is the essential question.  The real issue is whether privacy is extinct.

The reality today is that whether it is our government, another government, organized crime, commercial entities, or private parties - any communication that is encoded or may be captured in electromagnetic form (e.g. the sound of Selectric typeball rotating and striking paper) is subject to compromise - depending on the creativity, computing capacity, sophistication, motivation, and budget of the intercept and processing agents.

We can shield the rooms in which communications are prepared, encrypt our message prior to leaving the room, and use transmission technologies that minimize the probability of interception without notice.  But, in the end all we are doing is increasing the time  required to decode our message and thereby increasing the time/cost of the compromise process.

While the line for a regulated entity like the NSA may be set by Congress,  ultimately, all we accomplish by setting that line is tying their hands relying on what may well be an outdated sensibility regarding the concept of personal privacy given todays technological realities.

Perhaps it is time to stop handicapping our intelligence agency intercept and decoding;  rather establish limits for exchange of intel data similar to limits on exchange of personal medical data thereby supporting intelligence needs while protecting personal privacy.

I don't particularly care what our government knows about me.  They already have far more history than anyone else including even my closest friends.  Perhaps the key here may be to protect officially sanctioned intel data from misuse for unauthorized purpose.

Of course, we would have to do a better job protecting intel data from rogue agents like Edward Snowden and people who cleared, managed, and failed to detect his activities.

Warmest Regards, Sandy

I tend to lean the way of if you have nothing to hide and are doing nothing wrong who cares. If it will help this great nation to be safe then I'm all for it.