Three weeks before becoming president, Donald Trump weighed in on the threat of North Korea developing a nuclear warhead capable of reaching the U.S.: “It won’t happen,” he vowed on Twitter.

Now planners are contemplating what a U.S. strike to prevent that development might look like, and the options are grim.

Analysts estimate North Korea may now possess between 10 and 25 nuclear weapons, with launch vehicles, air force jets, troops and artillery scattered across the country, hidden in caves and massed along the border with South Korea. That’s on top of what the U.S. estimates to be one of the world’s largest chemical weapons stockpiles, a biological weapons research program and an active cyberwarfare capability.

And with Seoul and its 10 million residents just 35 miles (56 kilometers) south of the border — well within North Korea’s artillery range — any eruption of hostilities could have devastating human and economic costs. That’s why the North Korean dynasty founded by Kim Il Sung has long hinged its survival, in part, on a warning that any attack could provoke all-out war.

“Unless you were in a crisis situation where we thought the North Koreans were getting ready to attack us, a preemptive strike against the North Korean nuclear and missile program is simply not a practical option,” said Gary Samore, a former White House coordinator for weapons of mass destruction, proliferation and terrorism, who’s now at Harvard University’s Belfer Center. “This has always been the problem for the U.S. and our allies.”

After Trump ramped up his rhetoric against North Korea this month, the Pentagon ordered the USS Carl Vinson to head toward Korean waters, where the aircraft carrier is expected to arrive next week after some initial confusion in the administration on when it would go. Trump has warned that if China — North Korea’s closest ally — can’t help rein in the regime, the U.S. and its allies will.

The aircraft carrier USS Carl Vinson.

Photographer: Sean M. Castellano/U.S. Navy via Getty Images

U.S. Vice President Mike Pence, who is meeting with allies in Asia this week, said in an interview with CNN airing Wednesday that he doesn’t see the possibility of direct talks between the U.S. and North Korea “at this time.” He also declined to comment on whether or not U.S. sabotage was behind the failure of North Korea’s latest missile test.

Among the war-game scenarios at the Pentagon’s disposal are an airstrike using precision-guided munitions, launched from submarines or stealth aircraft, against the Yongbyon nuclear reactor facility, where North Korea has produced plutonium for its bombs. That was an option weighed as far back as the Clinton administration, according to two former Pentagon chiefs.

“We were highly confident that it could be destroyed without causing a meltdown that would release radioactivity into the air,” Ash Carter and William Perry wrote in a report for the Belfer Center back in 2002. That plan was seen as a worst-case scenario.

Stealth Bombers

Another option would be an attack on facilities at Punggye-ri, the mountainous site in the northeastern part of the country where previous underground nuclear tests have been conducted. 38 North, a website that focuses on North Korea, said satellite images signal recent activity in preparation for another nuclear test. Evading radar, B-2 bombers built by Northrop Grumman Corp. could drop “bunker buster” bombs to try to do the most underground damage.

A satellite image of the Punggye-ri nuclear test site on April 2.

Photographer: DigitalGlobe/38 North via Getty Images

Or, if the U.S. learned that North Korea was preparing to test an intercontinental ballistic missile — and it had confidence in where that missile would be launched — it could take out the vehicle, or try to shoot it down.

That probably wouldn’t save Seoul from devastation if North Korea responded to such a strike with a barrage of artillery or shorter-range missiles. In its defense, South Korea would go after the artillery that North Korea has massed near the demilitarized zone and use its Patriot missiles and anti-missile ships. In its final months, the Obama administration agreed to deploy a missile defense system known as Thaad to South Korea, but that shield isn’t fully installed yet.

The decision to attack isn’t Trump’s alone. Because South Korea would bear the brunt of any North Korean response, the highest levels of the South Korean military and government would “all have a say in making momentous decisions” like “do we or do we not go to war,” said Bill McKinney, a retired Army colonel who spent more than 40 years involved in U.S.-Korea military relations and planning. CONTINUE…