It's hard to imagine what a telephone conversation between President Xi Jinping of China and U.S. President Donald Trump would be like. But one actually took place this week, after Mr. Trump had tweeted, "North Korea is looking for trouble. If China decides to help, that would be great. If not, we will solve the problem without them!"
American presidents and other foreign leaders have long wanted China to help solve the North Korean problem. But China is cautious when it comes to its rebellious neighbour and has been reluctant to rein it in, even in spite of its recent ballistic-missile tests and boasts of nuclear capability.
So Mr. Trump's undiplomatic tweet may have been useful. The same goes for the American aircraft carrier group – what Mr. Trump calls a very powerful "armada" – currently heading to the Korean peninsula.
Mr. Xi and Mr. Trump have now agreed by phone that "the denuclearization of the Korean Peninsula shall be achieved through peaceful means." Chinese media also report that Beijing has said that North Korea should not undertake a sixth nuclear test.
The inexperienced and blunt Mr. Trump has may have succeeded in getting China to be more forthright about the threat posed by North Korea.
Of course, Beijing's pronouncements could turn out to be empty. But after its previous silence on the subject, the fact alone that China now publicly recognizes that Kim Jong-un's nuclear-weapons program is a serious danger is progress.
It would be a miracle if Mr. Kim were to give up the nuclear weapons he already has. On Thursday, North Korea appeared to be heading toward a nuclear test or more missile test launches, as Mr. Trump's administration threatened to retaliate against such provocative actions. The more things change, the more Mr. Kim's regime remains the same.