Remember all the hoo-ha over Donald Trump’s summit in June with North Korea’s maverick dictator, Kim Jong-un? With typical immodesty, Trump proclaimed a historic diplomatic breakthrough. Overnight, his Love Island-style tryst in Singapore had made the world a better place. “Everybody can now feel much safer than the day I took office,” Trump tweeted. “There is no longer a nuclear threat from North Korea.”

Hogwash. North Korea is fast emerging as the definitive example of how Trump takes a pre-existing international crisis and makes it worse. Claiming negotiating skills and a political prescience he does not possess, lacking thought-through and coherent strategies and ignoring the experience of more knowledgeable predecessors, he crassly blunders into sensitive situations, loud mouth blaring. US policy in Iran, Syria and Palestine has been similarly, anarchically upended.

The shattering of the false hopes raised by Trump in Singapore has not taken long. In a letter delivered two weeks ago, Kim reportedly threatened to resume nuclear weapons and missile tests. Talks on denuclearisation of the Korean peninsula – the summit’s sole, vaguely tangible outcome – have stalled. Their future is “again at stake and may fall apart”, the letter said, because Trump had reneged on understandings reached with Kim and subsequently zig-zagged to a harder position.

In familiar knee-jerk fashion, Trump responded by scrapping a visit to North Korea by his secretary of state, Mike Pompeo. He then publicly blamed China, not his own muddled messages, for undermining the US-led sanctions policy of “maximum pressure”. The Pentagon then followed up by suggesting that joint allied military exercises in the Korean theatre – suspended by Trump in a high-handed and unreciprocated concession – might soon resume.

Quite how Trump expects the talks to succeed if he bans his top diplomat from talking is unclear. Exactly why Trump believes China – with much at stake in North Korea – will follow his lead on sanctions while he simultaneously wages a trade war on Beijing is a mystery. And how long can hekeep on pretending the nuclear menace is over, when the UN’s International Atomic Energy Agency reports authoritatively that it is not?

The implosion of Trump’s deceptive Korean “breakthrough” risks some dreadful consequences. One is the sabotaging of separate, commendable efforts by Moon Jae-in, South Korea’s president, to restore bilateral trust and cooperation. American bungling has thrown into question Moon’s planned visit to Pyongyang this month – and has certainly rendered it more difficult. Another key ally, Japan, has no illusions, dismissing Trump’s big triumph as a flop. North Korea continued to pose a “serious and imminent” threat, Tokyo has declared.

Trump’s over-reaching, and subsequent reneging, is likely to enrage the Pyongyang regime, where hardliners are already crying betrayal. Kim himself may feel humiliated by Trump’s failure to fulfil dangled promises about a peace treaty or formal diplomatic recognition. The result could be a redoubling of the north’s efforts to build weapons of mass destruction and a rapid reigniting of regional military tensions.

Donald Trump, right, takes hold of Kim Jong-un’s arm as they greet each other in Singapore. Photograph: Evan Vucci/AP

Most dangerously of all, faced by the imminent collapse of his signal diplomatic “achievement” and worried about his standing among supporters ahead of November’s mid-term elections, Trump may revert to his previous, reckless posture. It is less than a year since he threatened to “totally destroy” North Korea by raining “fire and fury” on its civilian population. If Trump goes rogue again, there may be no coming back this time.

For now at least, US diplomats say they are not giving up on denuclearisation and detente. And it may be that Kim is playing hardball in a bid to win more concessions prior to resuming talks. But such calculations ignore Trump’s volatile temperament and aggressive instincts. He could lose it at any moment. Meanwhile, it’s vital to nail the lie, promulgated on the Republican right, that his chaotic foreign policy is working.

The deleterious impact of the “Trump effect” on other international hotspots can be seen in Palestine, where his funding cuts and tilt towards Israel over Jerusalem have rendered the peace process moribund. It is evident in Syria, too, where Russia’s bombers, unbelievably, have been given free rein; and in Iran, the undeserving target of unrestrained, highly provocative (and arguably illegal) American economic warfare.

Trump, who continues to address tweets to his supposed pal “Chairman Kim” is not the first American president to personalise foreign policy, convinced that he, uniquely, has the insight and charisma required to solve problems others believe insoluble. In maintaining, without any evidence, that he alone knows how to “handle” Kim, Trump follows in the footsteps of Franklin Roosevelt, who nurtured a similar conceit about Joseph “Uncle Joe” Stalin. In the event, as the historian Antony Beevor has recorded, Stalin ran rings around Roosevelt in 1945 when negotiating the postwar European order. Trump’s naive and egotistic blundering threatens more made-in-America disasters from east Asia to the Middle East and Europe.

• Simon Tisdall is a foreign affairs commentator