John Bolton — a Fox News contributor and former UN ambassador — is set to replace H.R. McMaster as President Donald Trump's national security advisor.



Bolton has long argued for a preemptive strike on North Korea in response to its nuclear-weapons program.



However, such a move would put South Korea, Japan, and US military installations at risk of an overwhelming retaliatory barrage by North Korea.



Defense experts estimate that in a best-case scenario for any strike, including in a "bloody nose" attack, more than 300,000 people in South Korea could die.



President Donald Trump has offered John Bolton, a Fox News contributor and former ambassador to the United Nations, the role of national security advisor.

The development comes following this week's resignation of former national security advisor H.R. McMaster.

"I humbly accept his offer," Bolton, who also works for the American Enterprise Institute, a conservative think tank, tweeted Thursday night. "The United States currently faces a wide array of issues and I look forward to working with President Trump and his leadership team in addressing these complex challenges in an effort to make our country safer at home and stronger abroad."

However, defense and arms control experts have expressed extreme reservations about slotting Bolton into this role, which he is slated to begin April 9. One arms control expert even labeled the appointment a "pretty much a national security emergency."

A major concern is Bolton's long-held and recently promoted views in support of a preemptive strike on North Korea. He appears ready to use force in attempt to halt North Korea's development of nuclear weapons and intercontinental ballistic missiles.

"It is perfectly legitimate for the United States to respond to the current 'necessity' posed by North Korea's nuclear weapons by striking first," Bolton wrote in a Feb. 28 opinion piece published by the Wall Street Journal.

Bolton went even farther during a September 2017 segment on Fox News: "The only diplomatic option left is to end the North Korean regime by effectively having the South take it over."

Yet defense experts say any preemptive attack would trigger an overwhelming retaliatory response from North Korea against South Korea, Japan, and US military installations.

According to conservative estimates, hundreds of thousands of South Koreans would die within hours, and possibly millions of people in the region if North Korea were to deploy nuclear weapons.

How a preemptive strike on North Korea could end in disaster

A North Korean ballistic missile test. KCNA via Reuters

There are two different violent responses North Korea could choose if the US were to attack. One option would be to use conventional artillery weapons — such as explosive mortars and rockets — and possibly chemical weapons like VX nerve gas. North Korea is known to have many reinforced bunkers armed with such munitions.

Kori Schake, who studies military history and contemporary conflicts at the right-leaning Hoover Institution, discussed this possibility on a Nov. 17 episode of the Pod Save The World podcast.

"[Suppose] in the space of, say, three hours, we could destroy all of the 8,000 to 10,000 hardened sites of North Korean artillery that Seoul, South Korea, is in range of," she said. "Even in that [scenario] — which would be a level of military virtuosity unimaginable — you're still probably talking 300,000 dead South Koreans."

The second option would be much worse: North Korean leaders could potentially deploy and launch the short-range nuclear weapons that the country has developed.

"[I]f the 'unthinkable' happened, nuclear detonations over Seoul and Tokyo with North Korea's current estimated weapon yields could result in as many as 2.1 million fatalities and 7.7 million injuries," Michael J. Zagurek Jr. wrote in an October 2017 analysis for 38 North, a project of the The US-Korea Institute at Johns Hopkins School of Advanced International Studies.

This is because Seoul's 25 million residents, including tens of thousands of US forces, are just 35 miles from the North Korean border. The death and injury figures do not take into account the loss of life north of the Korean Demilitarized Zone.

Jeffrey Lewis, a nuclear policy expert at the Middlebury Institute of International Studies at Monterey, previously told Business Insider that he doesn't think North Korea "would ever deliberately use the nuclear weapons unless they thought they were being invaded."

A map of the Korean Peninsula and the surrounding region. Google Maps

Lewis — who publishes Arms Control Wonk, a site about nuclear arms control, disarmament, and nonproliferation — and many other experts worry about how North Korean leader Kim Jong Un would respond to any kind of attack, perceived or real.

"The North Koreans, when they write official statements about what their nuclear posture or doctrine is, the phrase they use is 'deter and repel,'" he said, explaining that the country's nuclear arsenal has become its primary way of deterring conflict.

"But 'repel' means if the deterrent fails, and the United States launches an invasion, they will use nuclear weapons to try and repel the invasion — to try to destroy US forces throughout South Korea and Japan."

It remains to be seen how Bolton's coming appointment will influence pending denuclearization talks between North Korea, South Korea, and the US.

A spokesperson for Bolton declined to comment for this story.

This story was updated with new information. It was originally published at 12:08 p.m. EDT on March 23, 2018.