I hear a lot of venting on how we should have/could have stopped this [here and in many other places]...but the question that still remains unanswered...is how?
Rep. King (R-NY) wants to label Wikileaks a Foreign Terrorist Organization. That sounds great at first glance, except an actual link with terrorism has to have been established for that to transpire.
An option might be to invoke the International Emergency Economic Powers Act (IEEPA). This requires the President to declare a national emergency with respect to a foreign threat, and Treasury can take it from there.
FISA could come into play, but this is usually reserved for state entities, with exceptions for terrorism.
Wikileaks is a non-state foreign group not engaged in terrorism, so the legal recourse is murky. And as much as we have to maintain some level of secrecy, transparency is paramount for a democracy, so this event brings up an interesting academic discussion that otherwise wouldn't have taken place.