“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.
.. 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.
Some of Mr. Trump’s allies argue that his behavior is strategic, a way of telegraphing to North Korea — and to its primary patron, China — that the United States is taking a tougher line under this administration. There may be wisdom, they argue, in spurring fear and confusion in the mind of a leader who frequently relies on both.