The Winter Olympics’ closing ceremonies also concluded North Korea’s propaganda effort to divert attention from its nuclear-weapons and ballistic-missile programs. And although President Trump announced more economic sanctions against Pyongyang last week, he also bluntly presaged “Phase Two” of U.S. action against the Kim regime, which “may be a very rough thing.”

CIA Director Mike Pompeo said in January that Pyongyang was within “a handful of months” of being able to deliver nuclear warheads to the U.S. How long must America wait before it acts to eliminate that threat?

Pre-emption opponents argue that action is not justified because Pyongyang does not constitute an “imminent threat.” They are wrong. The threat is imminent, and the case against pre-emption rests on the misinterpretation of a standard that derives from prenuclear, pre-ballistic-missile times. Given the gaps in U.S. intelligence about North Korea, we should not wait until the very last minute. That would risk striking after the North has deliverable nuclear weapons, a much more dangerous situation.

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Although the Caroline criteria are often cited in pre-emption debates, they are merely customary international law, which is interpreted and modified in light of changing state practice. In contemporary times, Israel has already twice struck nuclear-weapons programs in hostile states: destroying the Osirak reactor outside Baghdad in 1981 and a Syrian reactor being built by North Koreans in 2007.

This is how we should think today about the threat of nuclear warheads delivered by ballistic missiles. In 1837 Britain unleashed pre-emptive “fire and fury” against a wooden steamboat. It is perfectly legitimate for the United States to respond to the current “necessity” posed by North Korea’s nuclear weapons by striking first.