“I have absolute right to do what I want to do with the Justice Department,” he said, echoing claims by his supporters that as president he has the power to open or end an investigation. “But for purposes of hopefully thinking I’m going to be treated fairly, I’ve stayed uninvolved with this particular matter.”

Hours after he accused the Chinese of secretly shipping oil to North Korea, Mr. Trump explicitly said for the first time that he has “been soft” on China on trade in the hopes that its leaders will pressure North Korea to abandon its nuclear weapons program.

He hinted that his patience may soon end, however, signaling his frustration with the reported oil shipments.

“Oil is going into North Korea. That wasn’t my deal!” he exclaimed, raising the possibility of aggressive trade actions against China. “If they don’t help us with North Korea, then I do what I’ve always said I want to do.”