Has data mining by the NSA breached our reasonable expectation of privacy under the Constitution's 4th amendment?
This is, of course, a matter of opinion. Until or unless the Supreme Court rules on this issue, there is no way to tell in an objective way if the NSA’s actions (or those that we know about, at least) actually do violate our right to privacy. My own view, which is of course based only on what is known to this point, is that the NSA’s actions do not breach our expectation of privacy. However, this is only an informed opinion, not an objective fact.
I would argue that the sort of data that the NSA have been collecting are not truly private. When we call someone, we have no reason to expect that the existence of the call itself will be private. We know that the phone company will keep records of who we call, when we call, where we are, and how long we talk. When we go on the internet, we know that there will be all sorts of evidence of what we have looked at and to whom we have sent emails. We know that all of these invasions of our privacy exist and yet we voluntarily engage in these activities.
Therefore, in my view, the government’s data mining does not infringe on our expectation of privacy. When we do things and we know that records of those actions will be kept, we are essentially giving up our right to expect that those actions will be private.