His new chief of staff and his national security team have drawn a line at trying to rein in his more incendiary provocations, fearing that their efforts could backfire with a president who bridles at any effort to control him. What remains unclear — and the source of much of the anxiety in and out of the government and on both sides of the Pacific — is whether they would step in to prevent the president from taking the kind of drastic action that matches his words, if they believed it was imminent.

Veterans of diplomacy and national security and specialists on North Korea fear that, whatever their intended result, Mr. Trump’s increasingly bellicose threats and public insults of the famously thin-skinned Mr. Kim could cause the United States to careen into a nuclear confrontation driven by personal animosity and bravado.

“It does matter, because you don’t want to get to a situation where North Korea fundamentally miscalculates that an attack is coming,” said Sue Mi Terry, a former intelligence and National Security Council specialist who is now a senior adviser for Korea at Bower Group Asia. “It could lead us to stumble into a war that nobody wants.”

And while his bombast may be a thrill to Mr. Trump’s core supporters, there is evidence that the broader American public does not trust the president to deal with North Korea, and is deeply opposed to the kind of pre-emptive military strike he has seemed eager to threaten.

A new Washington Post-ABC News poll found that 37 percent of adults trust Mr. Trump “a great deal” or “a good amount” to responsibly handle the situation with North Korea, while 42 percent trust him “not at all.” By contrast, 72 percent trust American military leaders, who have largely avoided combative language on North Korea even as they have said publicly that a military option is possible.