Ex attorney generals argue that the AP investigation was justified.

From the NYT:

While neither we nor the critics know the circumstances behind the prosecutors’ decision to issue this subpoena, we do know from the government’s public disclosures that the prosecutors were right to investigate this leak vigorously. The leak — which resulted in a May 2012 article by The A.P. about the disruption of a Yemen-based terrorist plot to bomb an airliner — significantly damaged our national security.

The United States and its allies were trying to locate a master bomb builder affiliated with Al Qaeda in the Arabian Peninsula, a group that was extremely difficult to penetrate. After considerable effort and danger, an agent was inserted inside the group. Although that agent succeeded in foiling one serious bombing plot against the United States, he was rendered ineffective once his existence was disclosed.

. . . The decision was made at the highest levels of the Justice Department, under longstanding regulations that are well within the boundaries of the Constitution. Having participated in similar decisions, we know that they are made after careful deliberation, because the government does not lightly seek information about a reporter’s work. Along with the obligation to investigate and prosecute government employees who violate their duty to protect operational secrets, Justice Department officials recognize the need to minimize any intrusion into the operations of the free press.