In recent weeks, North Korea has tested missiles and weapons systems that violate United Nations Security Council sanctions. U.S. President Donald Trump dismissed their importance. Pyongyang has criticized U.S.-South Korea military exercises, and Trump seemed to side with North Korea. Indeed, Trump’s remarks were part of a broad-based challenge to the very rationale of the U.S. alliance with South Korea, a view that Japan, for all its current difficulties with Seoul, finds disturbing and unfounded. Japan, like many other nations, is increasingly confronted by an unnerving question: Does Trump remain committed to U.S. alliances?

North Korea has conducted five rounds of weapons tests since late July. The most recent tests involved two short-range ballistic missiles, which flew about 400 km before landing in the Sea of Japan. They followed tests of multiple rocket launchers. Experts have concluded that the tests demonstrate marked improvements in North Korean capabilities: The use of solid fuel and mobile launchers suggests that Pyongyang has weapons systems that are easier to hide, move and fire. South Korean sources likened the missiles to a Russian missile that is highly maneuverable and better able to evade missile defenses.

Trump minimized the significance of the North Korean launches, noting that “These are short-range missiles. We never discussed that. We discussed nuclear. A lot of other countries test that kind of missile also.” His lack of concern is striking: Even the South Korean government, which is eager to engage Pyongyang, admitted that the most recent tests involved short-range ballistic missiles which are banned by U.N. resolutions.

Trump added that North Korean leader Kim Jong Un, in a “very beautiful” three-page letter to him, had offered a “small apology” for the tests and said they would end as soon as U.S.-South Korea joint exercises are over. Worryingly, Trump seemed to echo Kim’s description of the exercises as “ridiculous and expensive.” Trump complained that “We get virtually nothing” from South Korea and later tweeted that the South Korean government had agreed to “substantially” increase its contribution for the costs of U.S. forces in the country. In fact, Seoul has gradually increased its share of the cost of maintaining the 28,500 American military troops on its soil, agreeing last year to pay $925 million. New talks on cost sharing are about to resume. Tokyo must be ready for similar pressure when it begins its own negotiations with Washington over host nation support next year.

Pyongyang has long complained that U.S.-South Korea exercises are proof of Washington’s hostile intent, as they are practice for an invasion and thus justify its pursuit of a nuclear weapon program. North Korean propagandists now use the U.S. president’s own language to make that point. Kwon Jong Gun, director-general of the Department for American affairs at North Korea’s Ministry of Foreign Affairs, noted that “Even the U.S. president made a remark which in effect recognizes the self-defensive rights of a sovereign state, saying that it is a small missile test which a lot of countries do.”

Pyongyang is eager to drive a wedge between Washington and its Northeast Asian allies. One objective is to create insecurities in allied capitals, and convince them that the U.S. is not committed to their defense and therefore Tokyo and Seoul should do more to accommodate an increasingly well-armed North Korea. Trump’s seeming lack of concern about missiles that threaten those allies but cannot reach the U.S. homeland sends precisely that message. His determination to continue nuclear negotiations with Kim, and his apparent readiness to ignore any provocation or violation of international law or U.N. sanctions, are equally alarming.

U.S.-North Korea nuclear talks have stalled since the Hanoi summit earlier this year. U.S. officials believe they may resume after the military exercises conclude but Trump’s eagerness to strike a deal with Kim Jong Un undercut Pyongyang’s readiness to talk to anyone else in the U.S. government. Trump’s words trigger concern that he is ready to accept a North Korean nuclear capability as long as it cannot reach the U.S. homeland.

North Korea now insists that there can be no inter-Korean talks unless there is an end to the joint military exercises. Given Trump’s skepticism about exercises — and the fact that he suspended them after his first summit with Kim last year — it looks like Pyongyang may have a long-sought goal within reach: diminishing the effectiveness of the U.S.-South Korea alliance. That would have a profound effect on Japan’s security as it is tied to developments on the Koean Peninsula.

The emergence of a nuclear-armed North Korea when the U.S. military presence in Northeast Asia is shrinking is one of Japan’s worst fears. Trump must convince Japan and the world that he will not accept that outcome and that he remains committed to its allies in this part of the world.