Not as hard as media thinks
This is a case that does not look that hard to me, based on the way the Times wrote the stories. They refer to specific meetings with the President that had a very limited number of people in attendance, and they say that some of those people were their source for the material. While the easiest thing to do would be to making the reporters talk or go the jail as was done in the less important Plame case, I think they can question all the people at the meeting in question and probably find the source. If they lie, then they can squeeze the reporters and charge the source with a case similar to that brought against Scooter Libby. There has already been some speculation about who the person responsible for disclosing classified information might be.
Prospects are murky for the efforts of two prosecutors appointed by Attorney General Eric H. Holder Jr. to lead investigations into recent disclosures of government secrets.