President Trump, frustrated by China’s unwillingness to lean on North Korea, has told the Chinese leader that the United States is prepared to act on its own in pressuring the nuclear-armed government in Pyongyang, according to senior administration officials. Mr. Trump’s warning, delivered in a cordial but blunt phone call on Sunday night to President Xi Jinping, came after a flurry of actions by the United States — selling weapons to Taiwan, threatening trade sanctions and branding China for human trafficking — that rankled the Chinese and left little doubt that the honeymoon between the two leaders was over.
