WASHINGTON — President Trump named John R. Bolton, a hard-line former American ambassador to the United Nations, as his third national security adviser on Thursday, continuing a shake-up that creates one of the most hawkish national security teams of any White House in recent history.
Mr. Bolton will replace Lt. Gen. H. R. McMaster, the battle-tested Army officer who was tapped last year to stabilize a turbulent foreign policy operation but who never developed a comfortable relationship with the president.
The move, which was sudden but not unexpected, signals a more confrontational approach in American foreign policy at a time when Mr. Trump faces mounting challenges, including from Iran and North Korea.
The president replaced Secretary of State Rex W. Tillerson last week with the C.I.A. director, Mike Pompeo, a former Army officer and Tea Party congressman who has spoken about regime change in Pyongyang and about ripping up the Iran nuclear deal.
Mr. Bolton, an outspoken advocate of military action who served in the George W. Bush administration, has called for action against Iran and North Korea. In an interview on Thursday on Fox News, soon after his appointment was announced in a presidential tweet, he declined to say whether Mr. Trump should go through with a planned meeting with North Korea’s leader, Kim Jong-un.
General McMaster will retire from the military, ending a career that included senior commands in Iraq and Afghanistan. He had discussed his departure with Mr. Trump for several weeks, White House officials said, but decided to speed it up because questions about his status were casting a shadow over his exchanges with foreign officials.
Mr. Trump, the White House officials said, also wanted to fill out his national security team before his meeting with Mr. Kim, which is scheduled to occur by the end of May.
Mr. Bolton, who will take office April 9, has met regularly with Mr. Trump to discuss foreign policy. Though he has been on a list of candidates for the post since the beginning of the administration, officials said Mr. Trump has hesitated, in part because of his negative reaction to Mr. Bolton’s walrus-style mustache.
On Thursday, however, Mr. Trump summoned him to the Oval Office to discuss the job. Hours later, Mr. Bolton was on Fox, where he has been an analyst, for a pre-scheduled interview, in which he confessed surprise at how quickly Mr. Trump announced the appointment. “This hasn’t sunk in,” he said.
The news of the appointment competed with an exclusive interview on CNN of a former Playboy model, Karen McDougal, who described to Anderson Cooper what she said was a 10-month sexual relationship with Mr. Trump in 2006. Mr. Trump has denied the affair.
In his interview on Fox News, Mr. Bolton declined to discuss his views on Iran, Russia or North Korea, though he acknowledged his positions were hardly a mystery after years of writing and speaking. He described the job of national security adviser as making sure that the bureaucracy did not impede the decisions of the president.
Officials said that General McMaster’s departure was a mutual decision and amicable, with little of the recrimination that marked Mr. Tillerson’s exit. They said it was not related to a leak on Tuesday of briefing materials for Mr. Trump’s phone call with President Vladimir V. Putin of Russia, which infuriated the president and did not help General McMaster’s case. Mr. Bolton complained on Fox News…