The question is whether the leaks justified such an extensive invasion of journalists’ activities, with no advance notice and no independent oversight. That is exactly the kind of dispute a shield law is meant to resolve. Before compelling a journalist to testify or surrender records, the government would be obliged to meet the journalist’s lawyers in front of a judge. The prosecutors would have to make a good case that they had no other way to find the leak, that they would not cast their net so widely as to intrude on other reporting operations, and that identifying the leak was more important than the public value of the story. It’s not clear whether a shield law would have thwarted the government’s surveillance of The A.P. or Rosen. But it would have taken away the prosecutors’ power to decide unilaterally.

“Judges are not always wise,” Anthony Lewis wrote in 2007, endorsing the kind of compromise contained in Poe’s measure. “But in our system they are the ones we trust to weigh acutely conflicting interests.”

Sadly, the current Senate version of the shield law, which has been laboriously massaged to accommodate both media companies and secrecy hawks, has an intolerably large loophole for cases in which the government claims national security is at risk. That would leave the government with a free hand not only in the A.P. and Rosen cases, but in genuinely notorious revelations such as warrantless eavesdropping, secret prisons and torture, which would not have been disclosed without confidential sources.