AUSTIN, Tex.

SINCE February, the North Korean government has followed one threatening move with another. The spiral began with an underground nuclear test. Then the North declared the armistice that ended the Korean War invalid. The young dictator Kim Jong-un followed with a flurry of threats to attack civilian targets in South Korea, Japan and the United States.

Earlier this week, North Korea closed the Kaesong Industrial Complex, the only facility where citizens from North and South Korea work together. And now the North is openly threatening (and visibly preparing) to fire a mobile-launcher-based Musudan missile with a range that could reach many of the places Mr. Kim has menaced in his public statements. American intelligence agencies believe that North Korea is working to prepare even longer-range delivery systems to carry the nuclear warheads already in its arsenal.

The Korean crisis has now become a strategic threat to America’s core national interests. The best option is to destroy the North Korean missile on the ground before it is launched. The United States should use a precise airstrike to render the missile and its mobile launcher inoperable.

President Obama should state clearly and forthrightly that this is an act of self-defense in response to explicit threats from North Korea and clear evidence of a prepared weapon. He should give the leaders of South Korea, Japan, China and Taiwan advance notice before acting. And he should explain that this is a limited defensive strike on a military target — an operation that poses no threat to civilians — and that America does not intend to bring about regime change. The purpose is to neutralize a clear and present danger. That is all.