GEOFF BENNETT: For more on the national security implications, we turn now to Leon Panetta.

He served as secretary of defense and director of the CIA during the Obama administration, among many other roles in government.

Welcome back to the "News Hour," sir.

How does this lapse strike you from an operational security perspective, that the country's top national security officials shared information about an imminent strike, an imminent attack on a commercial messaging app?

LEON PANETTA, Former U.S. Secretary of Defense: Well, look, this is a serious security breach, particularly when it comes to war plans.

Look, war plans, attack plans are among the most sensitive and classified information that you can have.

And it has to be handled with care.

I think it was a mistake to have a conversation a Signal app that is not approved for sharing classified information.

So, I'm not sure why they even placed any of this information on Signal.

But, nevertheless, the fact that it included somebody who was not cleared for that information, and as a matter of fact was a member of the press, is a serious breach and one that needs to be fully investigated.

GEOFF BENNETT: What are the traditional secure channels for this type of discussion?

How would this normally unfold?

LEON PANETTA: Well, when I was both director of the CIA and secretary of defense, when it came to attack plans, the discussion was reserved for the Situation Room in the National Security Council, which is highly protected and is a place where you can have that kind of discussion without having to worry whether or not any of that information would leak.

So I'm a little bit taken aback that they would have this kind of conversation a commercial messaging network.

That just strikes me as being pretty careless.

GEOFF BENNETT: How might a foreign intelligence service, a foreign country trying to do the U.S. harm, how might they use this kind of information or how might they exploit what appear to be lax security practices?

LEON PANETTA: Well, there are very serious consequences to leaking information about a potential military attack.

If that information is leaked to an adversary, not only does it jeopardize very important intelligence resources that are being used to be able to determine military plans, but, in addition to that, that kind of leak would give a potential adversary an advantage of being able to strike first and going after whatever weapons, whatever naval vessels were going to be used for the attack.

So it could cost lives of our men and women in uniform if that information was leaked.

That's the danger here.

And, furthermore, it weakens our national security, very frankly, if we cannot protect that kind of sensitive information.

GEOFF BENNETT: President Trump, when he was asked about this today by reporters, he said he didn't know anything about it, and then he quickly pivoted to criticizing "The Atlantic."

It doesn't appear that he's focused on taking accountability.

And, of course, he faced a criminal trial, criminal charges from his handling of classified information.

That aside, in your view, what should the consequences be?

LEON PANETTA: Well, I don't think there's any question that somebody made a serious blunder here, a serious mistake, of including somebody that should not have been part of a national security group discussing war plans.

So, who added that name?

And why did that happen?

That really does have to be investigated, because it could involve a breach of our espionage laws, because that kind of breach simply cannot happen when the security of the United States is on the line.

That is the danger of having that kind of information leak.

GEOFF BENNETT: Former Secretary Leon Panetta, thank you for your time and for your insight, sir.

LEON PANETTA: Good to be with you.