Trump, asked if he considered North Korean leader Kim Jong Un to be rational, said he was operating from the assumption that he is rational. He noted that Kim had taken over his country at an early age.
"He's 27 years old. His father dies, took over a regime. So say what you want but that is not easy, especially at that age.
"I'm not giving him credit or not giving him credit, I'm just saying that's a very hard thing to do. As to whether or not he's rational, I have no opinion on it. I hope he's rational," he said.
Trump, sipping a Coke delivered by an aide after the president ordered it by pressing a button on his desk, appeared to rebuff an overture from Taiwan President Tsai Ing-wen, who told Reuters a direct phone call with Trump could take place again after their first conversation in early December angered Beijing.
China considers neighboring Taiwan to be a renegade province.
"My problem is that I have established a very good personal relationship with President Xi," said Trump. "I really feel that he is doing everything in his power to help us with a big situation. So I wouldn't want to be causing difficulty right now for him."
"So I would certainly want to speak to him first."
Trump also said he hoped to avoid a potential government shutdown amid a dispute between congressional Republicans and Democrats over a spending deal with a Saturday deadline looming.
But he said if a shutdown takes place, it will be the Democrats' fault for trying to add money to the legislation to "bail out Puerto Rico" and other items.
He also defended the one-page tax plan he unveiled on Wednesday from criticism that it would increase the U.S. deficit, saying better trade deals and economic growth would offset the costs.
"We will do trade deals that are going to make up for a tremendous amount of the deficit. We are going to be doing trade deals that are going to be much better trade deals," Trump said.