...The NSA may not, by its own charter, perform Communications Intelligence operations upon the United States or its citizens. It's target, and mission, is COMINT ops on foreign targets.
Now, I am certain the Administration will claim that the actual targets of this program are foreign terrorists. However, the one overriding law that the NSA must follow is the United States Signals Intelligence Directive (or USSID) 18. I would draw your attention specifically to the unredacted portions of Sections 4 and 5, which specifically deal with how communications collected from sources known to be US citizens are to be handled. I won't quote directly (you can read it all there) but in short, they can't. They are forbidden by federal law from collecting, processing and disseminating Signals Intelligence gathered from US Citizens.
And I don't really care how the Administration spins it, this meta-data collection and processing, especially as laid out in everything we've seen, is in direct contravention of USSID 18. And that makes it a federal crime.
Bonus question: What is the meaning of