Just a few weeks ago, Donald Trump was speculating that he might be awarded a Nobel Peace Prize, for his diplomacy with North Korea. But now the US president has abruptly cancelled his summit with Kim Jong Un, the North Korean leader.

The scrapping of the much anticipated meeting will raise fears of conflict once again on the Korean peninsula. Indeed both sides have resorted to chest-beating about their respective nuclear arsenals. On Wednesday, Choe Son Hui, a senior North Korean official, said it was up to the US, “whether it wants to meet us at a meeting room or encounter us at a nuclear-to-nuclear showdown”. The US president’s letter cancelling the summit responded: “You talk about nuclear capabilities, but ours are so massive and powerful that I pray to God they will never have to be used.”

There is now a serious risk that this rhetorical battle will escalate, returning the world to the period when President Trump was threatening North Korea with “fire and fury”. The risk of an escalation in the crisis is increased by the fact that Mr Trump’s new national security adviser is John Bolton, who has openly advocated military action against North Korea.