Secretary of State Rex Tillerson’s defenders argue that, while he may be an awkward public face for American diplomacy, behind the scenes he has been successfully building support among other countries for President Donald Trump’s policies. While U.S. Ambassador to the UN Nikki Haley may be adroit in her negotiations in New York, and a more congenial public speaker, the heavy lifting of government decisions happens in capitols and between foreign ministers, and that is where Tillerson has been quietly making a difference. The argument in Tillerson’s favor seemed to gain traction when China’s Central Bank announced it would be cutting off loans to companies doing business in North Korea and Tillerson’s comments in recent days suggesting lines of communication are open for direct negotiations with North Korea.

But then President Trump took time from his other pursuits to publicly castigate diplomatic efforts, tweeting “Save your energy, Rex, we’ll do what has to be done.” One cringes in embarrassment for Tillerson at this latest indignity suffered. But Rex Tillerson volunteered for this job, and stays by his own preference. More important than the personal humiliation are the very real risks that the Trump administration is exposing the country to through the president’s behavior: miscalculation, militarizing the North Korea problem, and, most importantly, missing the chance to prepare the American people for war.

If the Trump administration has a coherent policy toward the North Korean threat, I can’t discern it. The secretary of state says he is open to negotiations; the president says he is not. The national security advisor says the North Koreans cannot be deterred, yet the White House is threatening military action to deter them. Even the secretary of defense, the lodestar of sensibility in an otherwise chaotic administration, vacillates between saying America will respond to any North Korean attack against the U.S. or its allies, and that it will use military force against any threat to the U.S. and its allies. This may seem like a small, semantic difference, but those describe very different policies, one retaliatory and one preventative. And he made the preventative war statement following a meeting with the president, which may indicate it is the policy Trump himself supports. North Korea is a problem uncongenial to such messiness—the administration is leaving an awful lot of room for misunderstanding on a problem that admits little room for such mistakes.

This is the fifth or sixth time President Trump has indicated he is leading with the military option. He does seem deaf to the caution offered by every military expert from Clausewitz to Sir Robert G.K. Thompson, who in his brilliant book Regular Armies and Insurgencies teaches that "one of the very difficult things for a regular army to understand is that an undefeated army can lose a war.” Trump would do well to remember that America lost the last Korean War, and at great cost to ourselves and the Koreans. Did he not run for president complaining about the reckless hubris of the Bush administration for choosing a preventative war against Iraq? Militarizing foreign policy is also seldom advantageous for the United States, given the wide range of assets it brings to almost any foreign-policy problem. It is especially disadvantageous in the North Korean case because Washington doesn’t appear to have any good military options.

President Trump also tweeted “Being nice to Rocket Man hasn’t worked in 25 years, why would it work now? Clinton failed, Bush failed, and Obama failed. I won’t fail.” What the president of the United States seems not to grasp about the threat posed by North Korea is that the constraint on Presidents Clinton, Bush, and Obama, is the same one he faces. That constraint is the 30 million South Koreans and 130,000 Americans living within artillery and rocket range of North Korea’s conventional forces. Trump’s predecessors weren’t being nice to Pyongyang; they were recognizing that the risks of preventative war to remove the North Korean threat aren’t worth starting a war that will inevitably incur ghastly damage.

If President Trump is going to run those risks, he owes the American public and the world a much better explanation than he has given. The case he made in his UN General Assembly speech is only the first step in preparing Americans for a war that will produce grave risks to their safety, and inescapably bring devastation to the homelands of at least two treaty allies. One of the important reasons for engaging in diplomatic negotiations in advance of war is that it brings the public into greater understanding of the threats they incur, informs the policy conversation about the range of choice for dealing with the threats, and builds confidence that the commander-in-chief has a plan whose costs are commensurate with the risks.

It’s relatively easy to convince the American public to go to war. But it requires the president to invest his political capital in making the case repeatedly and diligently. By no means can intemperate tweets substitute for an extended conversation that persuades the American public (and preferably non-Americans, as well) of the necessity of war to achieve the country’s aims.

When presidents do not prepare the public for the consequences, the backlash is severe. President Clinton never regained the public’s confidence on national security after the Somalia debacle, in which Americans thought U.S. forces were delivering humanitarian assistance and found out they were, instead, fighting warlords. President Bush had to invest most of his second term in salvaging the Iraq war after underselling the difficulty U.S. efforts would face.

A preventative war against North Korea will be a war of choice for the United States. Diplomacy is an essential step in convincing the American public that the government has no choice less dangerous and damaging than war. President Trump forecloses that conversation at his peril; when the costs begin to accrue, he will wish he had bothered to bring the American public along because otherwise they will blame him for the consequences.