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.
Some senior administration officials acknowledge privately that Mr. Trump’s rhetoric on North Korea is not helpful, although they question whether it will alter the discussion, given how far Mr. Kim has come in his quest to develop a nuclear weapon that could reach the United States.
The three current and retired generals advising Mr. Trump — Jim Mattis, the defense secretary; Lt. Gen. H. R. McMaster, his national security adviser; and John F. Kelly, his chief of staff — as well as Rex W. Tillerson, the secretary of state, have all chosen their words on North Korea more carefully, emphasizing the role of diplomacy and the grave stakes of any military confrontation.
“All three of the generals fully realize the carnage that would result from a war on the Korean Peninsula,” James G. Stavridis, the former NATO commander and current dean of the Fletcher School of Law and Diplomacy at Tufts University, said on Sunday.
“Knowing each of them personally, I am certain they are counseling operational caution, measured public commentary and building a coalition approach to dealing with Kim Jong-un,” Mr. Stavridis, a retired admiral, said in an email. “But controlling President Trump seems incredibly difficult. Let’s hope they are not engaged in mission impossible, because the stakes are so high.”
Christopher R. Hill, a former ambassador to South Korea who served Republican and Democratic presidents, argued that the comments could badly undercut Mr. Trump’s ability to find a peaceful solution to the dispute, playing into Mr. Kim’s characterization of the United States as an evil nation bent on North Korea’s destruction and relieving pressure on the Chinese to do more to curb Pyongyang.
“The comments give the world the sense that he is increasingly unhinged and unreliable,” said Mr. Hill, the dean of the Josef Korbel School of International Studies at the University of Denver.
Mr. Hill, who as envoy to South Korea under George W. Bush was the last American to hold formal talks with the government in Pyongyang, said he and Condoleezza Rice, then the secretary of state, routinely advised Mr. Bush to “avoid the personal invectives,” because “they never help.”
“My sense from four years of those talks is that getting personal is not helpful,” Mr. Hill said. “Who could be telling Trump otherwise?”
Yet current and former senior officials said it was clear that Mr. Trump would continue his brinkmanship, particularly his belligerent tweets, no matter what his advisers do or say. One former administration official, who spoke on the condition of anonymity to discuss internal policy workings, said nobody, including Mr. Kelly, could control the president’s social media utterances, despite what his military advisers thought about them.
The tweets most likely have forced Mr. Mattis and Joseph F. Dunford Jr., the chairman of the Joint Chiefs of Staff, as well as other national security officials, to spend a significant amount of time on the phone reassuring counterparts about Mr. Trump’s intentions.