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President Trump seems to have absorbed at least one piece of advice from Barack Obama: North Korea’s nuclear program is a problem in urgent need of a solution. That was driven home on Tuesday when the North tested a missile that appeared to be capable of striking Alaska.

Mr. Trump may also be learning another lesson, that he can’t rely on China alone to force North Korea to rein in its nuclear program. What he hasn’t grasped is that a solution will eventually require direct dialogue with the North.

Mr. Trump has long insisted it is up to China, the North’s main food and fuel provider, to force North Korea to abandon its nuclear program, with its dozen or more nuclear weapons. And after a meeting with President Xi Jinping at Mar-a-Lago in April, Mr. Trump seemed confident that China would do so. But the intervening weeks have proved that China remains reluctant to exert the kind of pressure that could force the North to denuclearize. Beijing fears tough sanctions could destabilize North Korea, leading to the collapse of its government, chaos, a surge of refugees across the border and absorption of the country by South Korea, an American ally.

After Mr. Trump acknowledged in a recent tweet that depending on China “has not worked out,” his administration took steps that reflected his annoyance. It approved a $1.4 billion arms sale to Taiwan, which China considers a renegade province; it imposed sanctions on a Chinese bank accused of acting as a conduit of illegal North Korean financial activity; and an American naval destroyer passed near disputed territory claimed by China in the South China Sea. There is now talk of Washington moving on steel tariffs, which would be aimed partly at China.

Nudging China to ratchet up the pressure on North Korea is not a bad thing. But an outright break between the United States and China would very likely embolden North Korea. In a sign that neither leader wants to escalate tensions, Mr. Trump called Mr. Xi on Sunday to discuss North Korea, and Mr. Xi accepted the call. Mr. Trump warned Mr. Xi that America was prepared to act on its own in pressuring Pyongyang.

After the North’s missile test, the United States and South Korea held their own missile launch exercises. Secretary of State Rex Tillerson also announced plans to use traditional diplomatic tactics, including asking the United Nations Security Council to enact stronger sanctions and urging countries where North Korean workers are employed to stop “abetting a dangerous regime.” Mr. Trump spoke Monday about North Korea with the Japanese prime minister, held talks last week with the South Korean president and plans a dinner with both men in Germany on Thursday.

One hopeful sign has been an unofficial meeting between North Koreans and Americans in Oslo in May that included Joseph Yun, a senior United States diplomat, which led North Korea to release Otto Warmbier, an American student it had detained unjustly and treated outrageously. Mr. Warmbier died June 19 after being returned home in a coma. North Korea needs to give a full account of what happened. But contacts between officials of both countries should continue, both to seek the release of three other Americans and to build a foundation for future negotiations over the North’s nuclear and missile programs.