MARY LOUISE KELLY, HOST:

Let's stay with this story and bring in the voice of Frank Aum. He's a North Korea expert, formerly at the Defense Department, now at the United States Institute of Peace. And he's here in our studios. Welcome.

FRANK AUM: Thanks for having me.

KELLY: This idea of a bloody nose strike on North Korea, how seriously do you believe it is being considered as an option? And is it a good option for North Korea?

AUM: Well first of all, I think if the White House dropped Victor Cha as its nominee for ambassador to South Korea this late in the game because he expressed concerns about a military strike approach to North Korea, then that's very worrisome. It suggests that the White House is giving this option serious consideration.

KELLY: That they would not put an ambassador in place who was opposed to such an option.

AUM: Who can't advocate for that policy, correct.

KELLY: What's your personal take on it? Do you share the concerns that Victor Cha has raised?

AUM: I do. I think it's very problematic. I think first of all, how do you convince North Korea that we are only going for a limited bloody nose strike rather than trying to deliver a full knockout punch against the regime? That's a concern. So if North Korea thinks - I think - so Dr. Cha and many others have made this argument. They say that you can't assume on one hand that North Korea's so irrational that it can't be deterred and so we have to use military options against North Korea and then on the other hand, assume that North Korea is rational enough to not retaliate against a U.S. strike and escalate this into a full-blown war.

So if the U.S. strikes, then North Korea will have to respond to maintain its credibility and deterrence. And this means significant risks, huge human and economic casualties not only in Seoul but potentially in Japan and the United States as well.

KELLY: On the other hand, to play devil's advocate, diplomacy hasn't deterred North Korea. Sanctions don't appear to have done much to deter North Korea. Is there an argument to be made that something needs to be done to deter North Korea if the U.S. isn't prepared to live with a North Korea that can threaten mainland U.S. with nuclear weapons? Nobody's arguing this is the best case scenario.

But should it be on the table?

AUM: Well, first of all, North Korea has already been deterred and they have not conducted serious aggression against the United States or South Korea for over 60 years. North Korea is not suicidal. They know that any attack against the U.S. or its allies will result in their destruction. So we need to be aware of that, first and foremost.

I think we have to give President Trump some credit here that the maximum-pressure strategy is bearing some fruit. We've seen many countries shut down North Korean embassies, kick out diplomatic officials, which is helping to reduce North Korea's access to hard currency. China and Russia is getting on board in terms of adopting more serious stringent measures against North Korea, which has cut off almost - over 90 percent of North Korea's exports.

And even President Moon of South Korea has credited the pressure policy with getting North Korea to come to the table for the inner Korean talks, which has led to a period of peace leading up to and hopefully during the Winter Olympics period.

KELLY: Back to the saga of Victor Cha, the White House's original choice to be U.S. ambassador to Seoul. How big a void is it not to have an ambassador there?

AUM: Well, I first of all want to say that the Korea Foreign Service is doing a fantastic job and they're very able. Marc Knapper, who's the deputy chief of mission, is doing a wonderful job. That being said...

KELLY: They're running the embassy in the absence...

AUM: Correct. That's right.

KELLY: ...Of a personal ambassador - of a permanent ambassador.

AUM: Yes, very competent and capable. That being said, it's hard to substitute or achieve the level of stature that an ambassador has that has the full support of the president. So you need to have an ambassador in place to message the U.S. policy correctly and be the strongest advocate for what we're trying to accomplish on the Korean peninsula.

KELLY: In the few seconds we have left, given what has happened to Victor Cha, do you see other Korea experts raising their hand and volunteering for this post?

AUM: Well, if supporting a limited-strike option against North Korea as the litmus test, then I think that's very problematic for future ambassadorial nominees.

KELLY: So you're not raising your hand at this point.

AUM: No. No, I'm not.

KELLY: You're out of the running.

AUM: That's Frank Aum, senior expert at the U.S. Institute of Peace. Thank you very much.

KELLY: You're welcome. Transcript provided by NPR, Copyright NPR.