MOON JAE-IN is an optimist with an eye for symbolism. When the South Korean president travelled to Berlin in July 2017 to outline his strategy for easing tensions on the Korean peninsula, he insisted on speaking in a place that was associated with German unity. Only two days earlier, Kim Jong Un, the North’s leader, had tested his first intercontinental ballistic missile. But Mr Moon made an impassioned case for peace, hoping the room where officials from East and West Germany had negotiated the unification of their countries in 1990 would convey his dream of a united Korea.

The plan that Mr Moon outlined in Germany was easy to dismiss as rosy-spectacled. It included inviting a North Korean delegation to the Winter Olympics in South Korea, reviving reunions of separated families and possibly arranging a meeting between himself and Mr Kim. If that did not sound wishful enough, he also called on North Korea to give up its nuclear and missile programmes. In the ten months since then, however, much of what Mr Moon envisaged has become reality. Well, sort of.

On April 27th Mr Kim and Mr Moon met in the demilitarised zone (DMZ) between the two Koreas. Threats by North Korea to turn Seoul into a “sea of fire” were all but forgotten as Mr Kim made history—and melted South Korean hearts—by stepping over the dividing line, making him the first North Korean leader to enter the South since the end of the hot phase of the Korean war in 1953. The summit—only the third of its kind and the first in a decade—allowed many in the South to engage in a willing suspension of disbelief and see Mr Kim as an ebullient charmer, rather than a despot who runs the world’s most reclusive and repressive regime. The encounter, broadcast live, drew applause and tears of joy from South Koreans.

And there was more than just theatrics, or so it seemed. Days before the meeting Mr Kim had declared an end to his testing of long-range missiles and the closure of his nuclear test site at Punggye-ri in the north of the country. At the summit he told Mr Moon that South Korean and American experts—journalists even—would be invited to check that the Punggye-ri facility had indeed been closed. And North Korea would move to the same time-zone as the South. A peninsula that recently had seemed perilously close to a resumption of war was beginning, in the eyes of many observers in the South, to move closer to lasting peace. A poll conducted after the summit suggested that 65% of South Koreans trusted the North, up from just 15% before the meeting. A different poll found that Mr Moon’s approval rating had hit 86%, up from 73%. On social media, people began referring to Mr Kim as “cute”.

But experience has taught American officials harsh lessons about North Korean promises. The first and most basic: to cheer only concrete, verifiable actions by that country’s regime, and never its words. Veterans of talks with the North winced, therefore, when Donald Trump, America’s president, used a Rose Garden press conference on April 30th to ponder aloud where to fete his historic achievement, should his planned summit lead to peace.

Some aides had suggested neutral venues for the summit like Singapore, the president noted. But Mr Trump likes the DMZ because “if things work out, there’s a great celebration to be had, on the site.” To explain his showman’s sense that a “big event” could be in the offing, Mr Trump pointed to Mr Kim’s words, and specifically to the young dictator’s recent talk of ending nuclear testing, ballistic-missile launches and related research. He said Mr Kim had “lived up to that for a longer period of time than anybody has seen”.

Never mind the trivia

Actually, during previous cycles of promise-making and -breaking North Korea has sometimes gone two-and-a-half years between nuclear tests. Its most recent blast was less than six months ago. But details cannot slow Mr Trump when he senses a win in the offing for which he can take credit. And there yawns a great analytical divide between aides who serve Mr Trump today and veterans of previous talks with North Korea. When Team Trump contemplates the upcoming Trump-Kim summit, they see a historic event that will begin as a win for their boss—a vindication of his unprecedented toughness.

Asked on Fox News TV whether America can possibly trust Mr Kim, Mike Pompeo, the newly confirmed secretary of state, preferred to discuss a happier thought: that the young North Korean leader only “wants this meeting” because of Mr Trump and the international coalition he has assembled to put pressure on him. The same thought was echoed by Mr Trump’s hawkish new national security adviser, John Bolton. Reminded that he used to scorn the idea of deal-making with North Korea, Mr Bolton listed world leaders who have credited Mr Trump’s maximum-pressure campaign with bringing about the summit.

Other Americans who have lived through previous rounds of talks fear that the summit begins as a win for Mr Kim, not Mr Trump. Daniel Russel, a former senior diplomat and veteran of talks with the North, believes that the Kim regime’s goal, as so often before, is to seek acceptance from the world that North Korea is now a nuclear state. “For Kim Jong Un, summit day is his payday. He has landed a seat at the table as a peer,” says Mr Russel, now at the Asia Society. There are ways for a summit to lead to something worth celebrating, but they are slow and arduous, involving such steps as Mr Kim listing all of his nuclear and ballistic missile sites and agreeing a timetable for their inspection and eventual destruction.

Trump-sceptics worry that his hunger to strike a deal could lead him to accept far flimsier terms. Mr Trump insists that he will walk from the table if unsatisfied, and continue his policy of maximum pressure. But the coalition that created that pressure is crumbling. China rolled out the red carpet for Mr Kim in March, thawing relations after a deep chill. It fears being left out by Trumpian deal-making. As for last year’s American vows not to tolerate the development of North Korean nukes that could hit American cities, it is hard to imagine South Korea co-operating with pre-emptive American military strikes against the North, should the Kim-Trump summit end badly. Mr Trump is wondering where to celebrate a triumph. He will need luck and skill to avoid a debacle.