KIM JONG UN has shown what he thinks of President Donald Trump’s promise in early August to respond with “fire and fury” to North Korea’s growing nuclear threat. After pausing his missile tests just long enough for America’s secretary of state, Rex Tillerson, to say that Mr Kim was showing “restraint”, and for Mr Trump himself to claim to have Mr Kim’s “respect”, North Korea’s dictator unleashed three short-range missiles into the Sea of Japan. Most provocatively, on August 29th, an intermediate-range missile flew over Japan’s northern island of Hokkaido. Japanese under the missile’s path awoke to the sound of sirens, while the authorities urged them to seek shelter (see article). The missile crashed harmlessly into the Pacific 745 miles (1,200km) to the east, but Japan’s prime minister, Shinzo Abe, was right to call it an “unprecedented, serious and grave threat”. Only twice before, in 1998 and 2009, have North Korean missiles overflown Japan, when the regime used satellite launches to develop its missile technology. With this attack, the Japanese were reminded more than ever of their vulnerability. The rocket is likely to have been a Hwasong-12, a design with which, along with its intercontinental counterpart, Mr Kim’s scientists are making unexpectedly rapid progress. Previous launches of these missiles have sent them high into space and back into the sea. This test, for the first time, sent a missile on the kind of trajectory it would follow if used in anger. With each test, the scientists glean valuable data. They may already have learned to shrink a nuclear weapon enough to fit it on a missile, though a warhead may not survive re-entry. At this rate, North Korea could soon threaten to nuke anywhere from Seoul to San Francisco.

Calibrated unpredictability

It appeared to be a calibrated provocation—one intended not to invite a military response. That is a relief. Mr Kim has repeatedly threatened to launch tests in the direction of Guam, an American territory and military base, most recently after this week’s test. Mr Trump, who responded to the latest threat by appearing to rule out talks (and was immediately contradicted by his secretary of defence), remains open to military action. He should not be. A pre-emptive attack on the North’s nuclear sites would risk a cataclysmic response. Mr Kim might see it as an attempt to overthrow his regime, and react by raining destruction on Seoul, only 50km away from his massed artillery batteries. It is striking that in Japan and South Korea, many fear Mr Trump’s unpredictability even more than Mr Kim’s.

So how should America do right by its two East Asian allies? First, Mr Trump needs to understand the North’s plan, which is to drive a wedge between America and its friends in the region. Mr Kim’s calculation is that if he can threaten mainland America, he would make America think twice about intervening to protect South Korea or Japan. Would Mr Trump, whose slogan is “America First”, choose to sacrifice Seoul in the hope of saving San Francisco? Any hint of such thinking would undermine America’s alliances. If Japan and South Korea were to stop trusting American security guarantees, they might feel compelled to develop nuclear weapons of their own, alarming China and hugely complicating an already fraught situation.

So America must reaffirm and strengthen its commitment to defend its allies. Mr Trump could start by helping both Mr Abe and President Moon Jae-in of South Korea with extra missile defences, such as the new Aegis Ashore system. Mr Abe has been right to interpret Japan’s pacifist constitution more flexibly to enable him to help America. It would be better still for the alliance if Japan used its army like any other mature democracy, contributing fully to peacekeeping and joint-security operations. For now, public opposition to Japanese soldiers ever being shot at makes this hard. With luck, a future prime minister without the baggage of Mr Abe (whose grandfather, a hero of his, was accused of war crimes) could make it happen.

China and Russia, meanwhile, are not helping. Both countries have condemned Japan’s plans to upgrade its missile defences. That is callous and misguided; Japan has every right to defend itself against Mr Kim. China must stop encouraging North Korea by failing to apply UN sanctions strictly. And America should make clear that any threat to Seoul or Tokyo will be treated as if it is a threat to American territory. The chance of Mr Kim using his nuclear weapons is much smaller if he understands that to do so would spell the end of his regime, and his life.