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This is a rush transcript from "On the Record," February 6, 2015. This copy may not be in its final form and may be updated.

GRETA VAN SUSTEREN, FOX NEWS HOST: OK. Audience, is there any part of you that fears ISIS will come here or send someone here to the United States to kill? Whether it be a car bomb or something else lethal? Now that would be an "existential threat."

Here is what national security advisor, Susan Rice, just said while unveiling the new national security strategy.

(BEGIN VIDEO CLIP)

SUSAN RICE, NATIONAL SECURITY ADVISOR: But too often, what's missing here in Washington is a sense of perspective. Yes, there is a lot going on. Still, while the dangers we face may be more numerous and varied, they are not of the existential nature we confronted during World War II or during the Cold War.

(END VIDEO CLIP)

VAN SUSTEREN: Joining us, former U.N. ambassador to Iraq, Afghanistan, Syria and other countries, Ryan Crocker.

Good evening, Ambassador.

RYAN CROCKER, FORMER U.S. AMBASSADOR: Hello, Greta.

VAN SUSTEREN: So the -- as I understand, Susan Rice, she is saying what we are facing with ISIS is not the existential threat that we had with World War II, for instance. How do you define existential threat? Would that include the risk of a car bomb in Times Square? Is that an existential threat or not?

CROCKER: Greta, for me, existential threat means what it says, a threat to the existence of whomever that threat is aimed at. Certainly you can make the case that that's what we faced in World War II against the Axis. We don't face that against a terrorist group, whether it's al Qaeda and the World Trade Center or ISIS today. That said, they are a very grave threat indeed to us.

VAN SUSTEREN: So do you endorse her view that because it's not an existential threat, we should all take sort of a deep breath and -- I mean, these are my words, not hers -- and not be so alarmist?

CROCKER: Absolutely not. We never want to see a repeat of 9/11 or anything close to it. We have got to be all in, in this fight, to prosecute it over there so that it doesn't come back here to us. And I think there is every likelihood ISIS will seek to do just that, bring the fight on to American territory.

VAN SUSTEREN: You know, I don't know if I'm being an alarmist or being reasonable and practical. Unfortunately, I have to see if something happens to see whether or not you are alarmist or not, which is really regrettable. Even if you go back in history -- and you hear Neville Chamberlain name comes up a lot. In the spring of 1939, he said he spoke to Hitler, and Hitler was finished and wasn't going to go after anything at all. Lo and behold, by September, he was already moved into Poland. He said basically he had Hitler's word. It's so hard to predict into the future, you know, what's going to happen. How do you measure whether you are being patrol car continuing call and -- practical and smart and being tough or you are going to get hit hard? How do you tell that?

CROCKER: First, by erring on the side of caution. Assume it's real, it's lethal, and it's coming for us, until it's possible to demonstrate otherwise. We saw al Qaeda and what they did. This is an offshoot, an out group of al Qaeda. It was al Qaeda in Iraq, same leader then, same leader now, with Abu Bakr al Baghdadi. We have got to assume, just like al Qaeda, which has repudiated them for being too violent and too extremist, that they share though the same goal of coming here to fight.

VAN SUSTEREN: You know, it's interesting that not an existential nature, the threat, you know, after 9/11, you know, the United States didn't fall apart but the way we exists certainly did change. We have amped up all security. Can't even walk into an office building in Washington, D.C. without identification and signing in. You have got all that security at airports. Our lives really did change. And I actually see that as an existential threat to the United States, although the nation didn't fold. So I guess it's how you define existential threat.

CROCKER: It is. Our lives change all the time. They certainly changed after 9/11. Believe me, Greta, I know. I have been ambassador to Pakistan, Iraq and Afghanistan since 9/11. It certainly changed my life. But in no way was it a morality or even lasting blow to the America we know and love. We're stronger than that. We will face down any threat. We will go after them. I would like to see us in a position, and I think we are, by and large, to do everything we can to see that we disrupt any effort to come at us here.

VAN SUSTEREN: Well, I certainly don't want to be an alarmist but I also don't want to make the mistake of being too naive. And that's -- it's very difficult to look into the future on that one.

Ambassador, thank you, sir.

CROCKER: Thank you.