The DOJ got hold of the AP records without the wire service even knowing it happened, because the subpoena was to the phone companies instead of the journalists involved. While department guidelines require any news organization covered by a subpoena to be notified, there's an exemption if notification “would pose a substantial threat to the integrity of the investigation.”
Under the shield legislation, the DOJ could still delay notification of a covered journalist of a subpoena -- but only if a judge, not the administration, decided that disclosure would pose a substantial threat.
"The difference is that instead of DOJ unilaterally making that determination," the department would "have to convince a judge that this was the case," said University of Minnesota Law Professor Jane Kirtley.
The bill contains a large exception for national security, a compromise Obama pushed for back in 2009. In classified leak cases, a subpoena could not be quashed if the information would help prevent or mitigate an act of terrorism or other harm to national security. In a non-classified case, the reporter is not protected in those cases and if the information could help identify the perpetrator of an act of terrorism. Again, a court would decide.
The AP story at issue included details of a CIA operation in Yemen that foiled an al-Qaeda plot in spring 2012 to set off a bomb on an airplane headed to the United States.
Schumer himself made no claims that a shield law would have blocked the probe. Instead he says, "at minimum, our bill would have ensured a fairer, more deliberate process in this case."