North Korea’s nuclear weapons program is a global problem, and the threat should be met with an international response.

There was encouraging progress on Saturday when the U.N. Security Council — in a rare 15-0 vote — imposed severe economic sanctions on North Korea. If vigorously enforced, the restrictions would reduce the nation’s exports by about $1 billion, or nearly one-third.

The Security Council consensus was “a strong, united step toward holding North Korea accountable for its behavior,” said Nikki Haley, U.S. ambassador to the U.N.  Haley, who has been an admirable advocate for U.S. interests, showed that despite the discord often apparent in U.S.-Sino relations, China — North Korea’s enabling ally — can be convinced along with other countries that diplomacy is the best method to defuse Pyongyang’s nuclear threat.

But just days after the vote, President Donald Trump undercut this unity with reportedly unscripted and reckless rhetoric.

“North Korea best not make any more threats to the United States,” Trump said from his golf course in Bedminster, N.J. “They will be met with fire and fury like the world has never seen.”

Those words — literally and figuratively inflammatory — are unpresidential and unprecedented in the context of nuclear weapons. They’re also not strategic, because they threaten to fray the U.N. unity that was so diplomatically difficult to achieve. What’s more, Trump’s threat reframes, if not reverts, the nuclear dispute from an international issue to a bilateral, even personal, spat between the U.S. and North Korea and two erratic leaders.

The rhetoric could strain ties between the U.S. and South Korea, whose new leader, President Moon Jae-in, campaigned on a return to an engagement strategy with the North. Moon has been reticent to fully deploy a U.S. missile defense system, and Trump’s words may make Moon’s domestic political dynamics more difficult, as well as embolden Beijing to amplify pressure on Seoul to resist the defensive system that it considers a threat to China’s sovereignty.

Trump also risks establishing an unenforced “red line,” much like former President Barack Obama did regarding Syria — a move Trump harshly criticized. And sure enough, shortly after Trump’s statement, Pyongyang announced that it was “carefully examining the operational plan for making an enveloping fire at the areas around Guam.”

Credibility is essential in national security matters. Trump’s words, which reportedly were not vetted with the veteran generals who serve in his administration, threaten to further erode trust in the president.

“I think Americans should sleep well at night, have no concerns about this particular rhetoric of the last few days,” Secretary of State Rex Tillerson said on Wednesday.

That would be easier if Trump channeled Teddy Roosevelt. The U.S. already carries the big stick of military might. Now it needs to speak softly with world leaders on how to resolve this crisis peacefully.