It was only then — after pursuing “all reasonable alternative investigative steps,” as required by the department’s regulations — that investigators proposed obtaining telephone toll records (logs of calls made and received) for about 20 phone lines that the leaker might have used in conversations with A.P. journalists. They limited the request to the two months when the leak most likely occurred, and did not propose more intrusive investigative steps.

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.

While we cannot know all of the facts and considerations that went into the department’s decision, we do know that prosecutors were right to try to find out who gave this damaging information to The A.P. They were right to pursue the investigation with “alternative investigative steps” for eight months first. And ultimately, they were right to take it to the next stage when they still needed more to make a case against the leaker. If the Justice Department had not done so, it would have defaulted on its obligation to protect the American people.