This is serious first and foremost because the North Korean threat is serious. National Security Adviser H. R. McMaster is correct when he notes that the North Koreans have always been willing to sell anything—literally anything—to anybody with the hard cash to buy it. That will be true of their nuclear weapons. It is indeed true that Pyongyang is on the verge of acquiring the ability to obliterate Los Angeles, and eventually Washington. It is certain that this regime has shown no respect for any international norms, let alone international law; that it has committed murder; that it lives in a psychotic cocoon of its own making; and that it will stop at nothing. And it is true, finally, that this dangerous circumstance is not of Trump’s making: It is rather the consequence of policies that bought time and offered no idea what to do with the time that was purchased through shifting combinations of diplomacy, bribes, sanctions, and skullduggery.

Any administration faced with these facts, and at this technological moment in the North Korean program, would have weighed carefully the possibility of a preventive war —it would be the prudent strategic thing to do. And then that administration would have walked away from it. A deliberately initiated war still runs the risk of a humanitarian disaster because, as everyone now realizes, Seoul is within range of thousands of North Korean artillery tubes and rocket batteries. Hundreds of thousands of civilians, including American expats and dependents, would perish in the war that could be unleashed. Even assuming some magical technologies that enable the U.S. to disarm North Korea and decapitate its leadership, who is to say that the ensuing war would not have its way even so?

The consequences of preventive war—a war deliberately initiated by the United States or launched as a result of provocations by one side or both that then escalates—go far beyond this. South Korea, within the memory of people now living, has gone from being poorer than most African countries in 1950 to becoming a first-world technological and economic powerhouse. Could South Koreans forgive the Americans for the slaughter of their citizens and the devastation of their cities because of weapons aimed a hemisphere away? Would the Chinese meekly accept an American conquest of North Korea, or even simply the elimination of the Kim dynasty? Or are they more likely to pour troops, aircraft, and missiles into the Korean peninsula and to warn the Americans off? And where might that lead?

To judge by his public statements, McMaster, like United Nations Ambassador Nikki Haley, is hard over on the notion that North Korea has to be denuclearized, be it by peaceful surrender or by force. He has used the words preventive war on several occasions. In so doing he is, of course, echoing the president, but it is reasonable to think that he agrees with the basic idea. And that would not be entirely surprising: His duty is to ensure the security of the United States, and North Korea’s intercontinental ballistic missiles would undoubtedly be a threat to that.