The beautiful letters beguiled him

As North Korea fired off a series of missiles in recent months — at least 18 since May — President Trump has repeatedly dismissed their importance as short-range and “very standard” tests. And although he has conceded “there may be a United Nations violation,” the president says any concerns are overblown.

Kim Jong-un, North Korea’s leader, Mr. Trump explained recently, just “likes testing missiles.”

Now, American intelligence officials and outside experts have come to a far different conclusion: that the launchings downplayed by Mr. Trump, including two late last month, have allowed Mr. Kim to test missiles with greater range and maneuverability that could overwhelm American defenses in the region.

Japan’s defense minister, Takeshi Iwaya, told reporters in Tokyo last week that the irregular trajectories of the most recent tests were more evidence of a program designed to defeat the defenses Japan has deployed, with American technology, at sea and on shore.

Mr. Kim’s flattery of Mr. Trump with beguiling letters and episodic meetings offering vague assurances of eventual nuclear disarmament, some outside experts say, are part of what they call the North Korean leader’s strategy of buying time to improve his arsenal despite all the sanctions on North Korea.

The rapid improvements in the short-range missiles not only put Japan and South Korea in increased danger, but also threaten at least eight American bases in those countries housing more than 30,000 troops, according to an analysis of the missile ranges by The New York Times. Such missiles, experts say, could be designed to carry either conventional or nuclear warheads.

“Kim is exploiting loopholes in his agreements with President Trump pretty brilliantly,” said Vipin Narang, a political-science professor at M.I.T. who studies North Korean weapon advances. “These are mobile-launched, they move fast, they fly very low and they are maneuverable. That’s a nightmare for missile defense. And it’s only a matter of time before those technologies are migrated to longer-range missiles.”

President Trump says that Mr. Kim committed to him during a meeting in Singapore 14 months ago that he would refrain from testing intercontinental ballistic missiles and conducting nuclear tests while negotiations are underway, and he has kept those promises even though there have been no substantive talks since a second summit in Hanoi in February resulted in an impasse.

But North Korean state-run media made clear last week that the country feels no such limits when it comes to improving other missile technologies, saying it would never accede to the West’s demand “for disarmament under pressure and appeasement of ‘international society.’”