It's become difficult to muster surprise at the bad behavior of the NSA these days, but the first question that occured to me after learning the government is assembling a database of millions of Americans' phone calls was: how long before Seymour Hersh's sources are identified? Even as I considered the question, it seemed like a stretch. As ABC's Brian Ross and Richard Esposito report, apparently not.

A senior federal law enforcement official tells ABC News the government is tracking the phone numbers we (Brian Ross and Richard Esposito) call in an effort to root out confidential sources.

"It's time for you to get some new cell phones, quick," the source told us in an in-person conversation.

Josh Marshall points out that if these incidents of probing phone records (and many other records) occur in the context of a criminal leak investigation, it's perfectly ordinary and legal. But, Josh notes, the ABC News story hints at something more than discrete investigations.

In Ross and Esposito's follow up report, the source claims they were wrong to suggest reporters' phone calls were being "tracked."

"Think of it more as backtracking," said a senior federal official.

Uh huh. The FBI also responded:

In a statement, the FBI press office said its leak investigations begin with the examination of government phone records.

"The FBI will take logical investigative steps to determine if a criminal act was committed by a government employee by the unauthorized release of classified information," the statement said.

Officials say that means that phone records of reporters will be sought if government records are not sufficient.

The tool employed by the FBI to get at these records is something called a National Security Letter, which functions as a subpoena but doesn't bear a judge's signature. "Under the law [USA Patriot Act], a phone company receiving a NSL for phone records must provide them and may not divulge to the customer that the records have been given to the government."

This is the slipperiest of slopes. If Ross and Esposito are right and the government is gathering information on reporters' sources for "national security reasons" free of judicial oversight, how will the information gathered be used? Why should investigators confine their probe to "national security related" stories? Without accountability, what's to stop investigators from contacting sources? What's to prevent them from ruining the careers of investigative journalists?

In other words, what, exactly, doesn't the war-on-terror justification cover? Raising taxes?

UPDATE

Brian Ross continues to follow the story:

The Department of Justice says it secretly sought phone records and other documents of 3,501 people last year under a provision of the Patriot Act that does not require judicial oversight.

The records were obtained with the use of what are known as National Security Letters [NSLs], which can be signed by an FBI agent and are only for use in terrorism cases.

(snip)

Assistant Attorney General William Moschella told Congress last month that 9,254 National Security Letters were issued in 2005 involving 3,501 people.

Last year, the Washington Post reported that the FBI issues more than 30,000 NSLs a year:

Senior FBI officials acknowledged in interviews that the proliferation of national security letters results primarily from the bureau's new authority to collect intimate facts about people who are not suspected of any wrongdoing. Criticized for failure to detect the Sept. 11 plot, the bureau now casts a much wider net, using national security letters to generate leads as well as to pursue them. Casual or unwitting contact with a suspect -- a single telephone call, for example -- may attract the attention of investigators and subject a person to scrutiny about which he never learns.

A national security letter cannot be used to authorize eavesdropping or to read the contents of e-mail. But it does permit investigators to trace revealing paths through the private affairs of a modern digital citizen. The records it yields describe where a person makes and spends money, with whom he lives and lived before, how much he gambles, what he buys online, what he pawns and borrows, where he travels, how he invests, what he searches for and reads on the Web, and who telephones or e-mails him at home and at work.

In 2003, Barton Gellman explains, the Bush administration overturned the traditional policy of requiring agents to destroy files on innocent citizens. In December 2005, Bush signed Executive Order 13388, which opened those preserved files on innocent Americans to "state, local, and tribal" governments, and to "appropriate private sector entities." What private entities did the president mean? Halliburton? Starbucks? Citibank? The order doesn't say. Read the whole story.