On second thought...
Although it is unlikely, I'll tell you how it could happen. Most coverage is focused on the crime that may or may not have been committed in leaking information about Wilson's wife.
However, the basic facts about Wilson's trip to Niger were classified until Tenet's statement on July 11. I say that based on two pieces of evidence: the June 10 INR memo, which clearly indicated that some aspects of this trip were classified, and Karl Rove's cryptic comment to Matt Cooper on the morning that Tenet's statement was released - "Rove told me material was going to be declassified in the coming days that would cast doubt on Wilson's mission and his findings."
Well, then - any Administration official who gave a reporter information about the Wilson trip, or merely confirmed that a trip took place, is arguably guilty of leaking classified info.
Based on this TIME account, following the Walter Pincus article of June 12 there were lots of reporters asking lots of government officials about the Wilson trip. Newsday found "more than two dozen" journalists swept up in Fitzgerald's review of the administration contacts.
Now, let's accept that most of those conversations did not involve any discussion of Wilson's wife. So what? If they talked about Wilson's trip, the administration official could be charged.
From the Pincus article itself, we can find confirmation that candidates for prosecution on this basis are out there:
Armed with information purportedly showing that Iraqi officials had been seeking to buy uranium in Niger one or two years earlier, the CIA in early February 2002 dispatched a retired U.S. ambassador to the country to investigate the claims, according to the senior U.S. officials and the former government official, who is familiar with the event. The sources spoke on condition of anonymity and on condition that the name of the former ambassador not be disclosed.
Now, would Fitzgerald actually deliver these charges? Indicting people for leaking in June what was publicly disclosed in July may seem absurd.
On the other hand, it could be a potent bargaining chip. Keep it in mind.
As to indicting Wilson on this basis? Apparently he had not signed a non-disclosure agreement, and he is a private citizen, not a government official relying on his access to classified info. Pass.
UPDATE: In response to a reader revolt on the question of Wilson's clearance, I find this in the SSCI report (p. 41):
The CIA has told Committee staff that the former ambassador did not have a "formal" security clearance but had been given an "operational clearance" up to the Secret level for the purposes of his potential visit to Niger.
...DO officials told Committee staff that they promised the former ambassador that they would keep his relationship with CIA confidential, but did not ask the former ambassador to do the same and did not ask him to sign a confidentiality or non-disclosure agreement. The former ambassador left for Niger on February 21, 2002.
I'll admit to being baffled - does this mean he can be prosecuted even without a non-disclosure agreement? Personally, I would love to think so, but I remain a skeptic.
As to scenarios in which Joe and Valerie are indicted on the theory that Valerie was passing classified info to Joe, who then leaked it - yes, it would make my day. Kevin Drum had a theory which could have led to indictments; following Seymour Hersh's suggestion in "The Stovepipe" that the Niger documents were forged by ex-CIAers, I hinted at a conspiracy that included Joe. But at this point, I just don't see Fitzgerald blindsiding everyone by heading in this direction.
This comment captures a preaviling sentiment which I share:
I am not disputing that discussing the mere fact of Wilson's trip would be a technical violation of the law. I am saying such a result would be ludicrous! Wilson discloses to the world the nature and purpose of his trip. After that disclosure, government officials would violate the law by acknowledging that Wilson went on the trip? If so, Dickens was right: The law's an ass!
I suppose the answer is, Bush and Tenet should have formally declassifed the appropriate info and then rebutted Wilson. In other words, there should have been no leaks prior to Tenet's July 11 statement. As If.