My first reaction to the AP's disclosure that the Justice Department had subpoenaed two months worth of telephone call records (that is, for a certain number, the identity of the person called, and the duration of the call, as recorded by the telephone company) for 20 personal and professional phone lines leased by both reporters and editors, was one of sympathy for my journalistic kin.
Since May 2012, the Justice Department has been investigating the unauthorized disclosure of classified information that led to an Associated Press article about a failed bomb plot that ended with the U.S. taking custody of an IED bound for America.
On May 7, 2012, the AP ran its story; the perpetrator was in custody over the objections of the White House. Other parts of the national security machine were attempting to pursue the loose ends of the plot to see whom it might ensnare, and that effort was apparently cut short. As soon as it became clear that the AP was publishing its story, the White House tried to spin in, and John Brennan, then the chief counter-terrorism adviser to the president, held a background briefing for the media's go-to national security consultants, a fairly common practice. In the briefing, Brennan suggested that no real danger was posed to Americans because the U.S. had "inside control" of the investigation. On ABC News that night, Richard Clarke accurately read between the lines and stated that the government had a mole on the inside of the investigation.
Initially, when the White House complained about the leaks, the AP and others pointed to Brennan's disclosure; the original AP story didn't say a word about the mole. But that assumes that the fact of the investigation itself was classified, that the White House, acting under the authority of the president, essentially declassified the operation after the fact in order to control the spin, and that Brennan was operating in a familiar grey zone, where bits of sensitive information float around without having been formally declassified but generally assumed to have been declassified, or be deemed OK to release. There is no formal procedure for declassifying an "operation," especially since it would involve multiple agencies and multiple original classification authorities. That's why a "leak" to spin an already public fact from the National Security Council is generally tolerated by the law and by Congress so long as the White House seems to know what it's doing.
(Valerie Plame's status as a CIA officer was, of course, not a public fact, and not covered by this informal exemption. Neither is freelancing disclosures, of which there are many. Here I'm referring only to broad disclosures as a matter of policy as approved by the president.)
In this amorphous zone of declassification, the White House can pretty much decide on its own what constitutes national security information. And in the case of the AP story, it was the "fact" of the investigation and the "fact" that the government had taken the actual bomb into its custody. And "inside control," and whatever it implied, was not protected national security information, even if it led to a spate of stories reporting that the Brits and Saudi Arabia infiltrated al Qaeda in Yemen.
In a letter to the AP today, the Justice Department disclosed that it has conducted more than 500 field interviews and reviewed (tens of thousands of) documents before going to a court to obtain the toll records. The deputy attorney general suggested that the records requested do not cover the entire span of two months. The Justice Department contends that it fulfilled the requirements for seeking information from journalists: It gave the AP prior notice (i.e., a few seconds before, probably), it limited the scope "as narrowly as possible," and that attempting to negotiate with the AP to provide the information would have jeopardized parts of their investigation. The Justice Department also makes it clear that it didn't seek the "content" of the calls, although that would have required an active interception.
Why was this leak so bad, then? Why pursue these leakers so aggressively?
Because Brennan might have been implicated and may have spoken off the cuff or too hastily in his briefing, and because he was slated to be the president's next CIA director (everyone assumed this in Washington but it hadn't been confirmed), and because Congress demanded an investigation of this particular leak, and because (I'll grant) the information released could well have been harmful, a perfect storm arose, and the Justice Department found it had the political backing to aggressive and unflinchingly pursue the leakers.
Marcy Wheeler notes that the two-month period in question would (potentially) allow the FBI access to phone records of AP intelligence reporter Kimberly Dozier when Dozier was reporting several new details about a change in the way the White House manages its counter-terrorism targeting process. Congress, too, demanded an investigation into these leaks, even though the facts in question were very far removed from operational details that could conceivably harm national security.
In that case, Congress was mad because it was not told before someone gave the information to Dozier. Brennan took over this targeting process at the time the U.S. started "signature strikes" in Yemen and the administration made a concerted effort to rebut allegations that the careful targeting processes employed the Defense Department had been gutted. So at the same time as the FBI and CIA were wrapping up the "inside control" case in Yemen, a case that the White House was watching very closely, it was facing a frontal assault from the media and Congress about its counter-terrorism policies in general.