Whatever its difficulties, the United Nations must surely be cherished. Founded in 1945 under US leadership after the defeat of Nazism and imperial Japan, the UN remains the central pillar of the global order. At its core has stood the ambition that peace, international security and human rights would be better protected than they were by the 1930s League of Nations (whose founding treaty the US Senate refused to ratify). The UN is the only existing forum where the representatives of all nation states can be brought together to try to address crises and common challenges.

Donald Trump’s first address to the organisation’s annual general assembly was anticipated with dread by many – and rightly so. This US president is after all the first in history to have made heaping scorn on the UN something of a pastime. His views on the subject have ranged from crude hostility to abject ignorance. The speech he delivered was scripted – not the ramblings of a maverick whose taste for rash tweets and cheap provocations have become an almost daily routine. It was deeply worrying all the same. Unlike his eloquent predecessor, President Trump trades in crass belligerence. His speech will be remembered for its ominous language.

On North Korea he mocked its young leader Kim Jong-un, saying that “rocket man is on a suicide mission for himself and for his regime”. He threatened that “if [the US] is forced to defend itself and its allies, it will have no other choice but to destroy North Korea”. Iran, he said, was “a corrupt dictatorship” whose “chief export is violence, bloodshed and chaos”. Trump called the 2015 nuclear deal “the worse transaction ever” – a sign perhaps he may be getting ready to pull out of it, or ensuring Iran is provoked enough to do so itself. What the White House could have done is appeal to the Iranian people directly, offering a “new beginning” in the relationship between the two nations. But the US president has not displayed the slightest interest in fundamental democratic values. His speech carried enough of a whiff of “regime change” to make Tehran think hard over nuclear compliance.

As last week’s UN security council vote on sanctioning North Korea has shown, there is an international consensus on the dangers presented by Pyongyang’s behaviour. But on Iran, President Trump risks finding himself in stark isolation, with European allies already making clear they want to preserve the 2015 agreement, not tear it up. The US president no doubt speaks to his base as much as he does to an international audience. But the nationalist ideology he espouses was yet again made clear, not least with the emphasis he put on “strong, sovereign, independent nations”, rather than on the body of universal values that the UN is meant to uphold.

President Trump wants the UN to put pressure on North Korea and Iran, but he’s brought little clarity as to the wider strategy he contemplates. Threats and grandstanding are just bluster, not policy. Crises require a deftness the Trump administration has failed to demonstrate. He wants allies to back him, but seems oblivious that his lack of personal credibility is an obstacle to international cooperation. An “America First” approach runs counter to the UN’s multilateralism. His credo could be summed up by his claim that nations acting in their own self-interest create a more stable world. The question is what rules would states operate under? Not the UN’s, Trump’s response appeared to suggest. The president may want to speak of “principled realism”, but he is a reckless and dangerous leader, sitting, alas, in a most powerful position.