"Most of the time when there's a leak," said Martin, "whatever recriminations that are made within the government are made privately. It rarely gets to be subject of a story. What has really changed with the Bush administration is that these leak investigations are now spread exhaustively on the public record."
Martin cited the Valerie Plame case, the government's investigation into the leaking of the NSA eavesdropping story to the New York Times, and the CIA's investigation of leaks to the Washington Post about secret prisons.
What's particularly interesting about the potential House Intelligence investigation, said Martin, is that the information about the NIE that was disclosed to the New York Times was, within days, declassified by the government. "The government decided that it wouldn't harm national security so they declassified it. So the harm there [for the leaker] was in deciding on his or her own to put it out."
For the most part, said Martin, the disclosure of most classified information wouldn't necessarily pose a threat to national security. Often, it's just that no one has bothered to declassify it.
The threat of disclosure instead may be political, said Martin. "Either it's counter to the message – like the NIE, which was counter to the message that the Iraq war was making us safer."
The other possibility is that leaked information limits the government's "freedom of action," said Martin. "If [as a reporter] you don't know something is going on, then you're not asking them questions about it. Then they can take their time and make decisions without any outside pressure."
"Obviously we want full, real-time information and they want to reveal partial information with a significant time delay," he added.
While he can't draw a "one to one connection" between a leak investigation resulting in a hush on information from sources, Martin said "there's no question that [such investigations] have a chilling effect. They used to be a joke. They almost never found the leaker. Of course, that wasn't always true. I can think of two cases, that's in 20 years, and in both the person resigned or was reassigned" to a job with little access. "Let's say I'm forgetting one or two or there are people I don't know about. It's still a fairly rare occurrence."
"Now, whenever there's a big story based on a secret report," said Martin, "the next question is, 'Is there going to be an investigation?' They use tools they previously didn't use, determine who had access and then you get a universe of people who are suspects."
"And now, we're talking about monitoring e-mail, getting sworn statements and subpoenaing reporters. And that's really the way to find out the identity of a source, to say, 'OK, you have choice: you can go to jail or reveal the source. So far, one reporter has gone to jail," said Martin. "I think there's certainly going to be another."