WASHINGTON — President Trump named John R. Bolton, a hard-line former US 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.
Bolton will replace Lieutenant General H.R. McMaster, the battle-tested Army officer who was tapped as Trump’s second national security adviser last year to stabilize a turbulent foreign policy operation. But McMaster never developed a comfortable relationship with the president.
The move, which was sudden but not unexpected, signals a more confrontational approach in US foreign policy at a time when Trump faces mounting challenges from Iran and North Korea.
The president replaced Secretary of State Rex Tillerson last week with CIA 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.
Bolton, 69, an outspoken advocate of military action who served in the George W. Bush administration in a key arms-control job, has called for military action against Iran and North Korea. In an interview Thursday on Fox News, soon after his appointment was announced in a presidential tweet, he declined to say whether Trump should go through with a planned meeting with North Korea’s leader, Kim Jong Un.
McMaster will retire from the military, ending a career that included senior commands in Iraq and Afghanistan. He had discussed his departure with Trump for several weeks, White House officials said.
Trump, the officials said, is seeking to fill out his national security team before his meeting with Kim, which is scheduled to occur by the end of May.
Bolton, who will take office April 9, has met regularly with Trump to discuss foreign policy. Though Bolton has been on a list of candidates for the post since the beginning of the administration, Trump has hesitated, in part because of his negative reaction to Bolton’s walrus-like mustache, officials said.
On Thursday, however, Trump summoned him to the Oval Office to discuss the job. Hours later, Bolton was on Fox, where he has been an analyst, for a prescheduled interview, in which he confessed surprise at how quickly Trump announced the appointment. “This hasn’t sunk in,” he said.
On another key foreign policy question, Bolton has been even more hawkish than Trump on Iran, pushing for the president to withdraw from the nuclear agreement the United States and five other world powers reached with Tehran during the Obama administration.
In January, Bolton told Fox News that Trump should dump the nuclear deal, reimpose economic sanctions on Tehran, and work toward an overthrow of the government there.
‘‘There’s a lot we can do, and we should do it,’’ Bolton said. ‘‘Our goal should be regime change in Iran.’’ He similarly called for bombing Iran in a New York Times editorial in 2015.
McMaster’s departure and Bolton’s ascension will come about a month before a deadline for Trump to decide whether the United States will remain a party to the deal.
Bolton required a recess appointment for his position as US ambassador to the United Nations after Democrats and several Republicans blocked his nomination in 2005. He resigned the following year after Democrats had taken control of Congress and it was clear he could not be confirmed.
Old grievances resurfaced before Trump took office, when as president-elect he considered selecting Bolton as deputy secretary of state. That job would have been subject to Senate confirmation, and opposition to the potential choice was swift and bipartisan.
Bolton has maintained a pair of political committees, which he has used to funnel political support to hawkish candidates. The top donor to the groups was Robert Mercer, who has given $5 million to Bolton’s super PAC in recent years, the Associated Press reported.
Democrats greeted the news about Bolton with deep alarm. “The person who will be first in, first out of the Oval Office on national security matters passionately believes the US should launch preemptive war against both Iran and North Korea with no authorization from Congress,” said Senator Chris Murphy of Connecticut. “My God.”
Republicans expressed satisfaction. “Selecting John Bolton as national security adviser is good news for America’s allies and bad news for America’s enemies,” said Senator Lindsey Graham of South Carolina.
McMaster struggled for months to impose order not only on a fractious national security team but on a president who resisted the sort of discipline customary in the military. Although McMaster has been a maverick voice at times during a long military career, the Washington foreign policy establishment had hoped he would keep the president from making rash decisions.
Yet the president and the general, who had never met before Trump interviewed McMaster for the post, had little chemistry, and often clashed behind the scenes.
Their tensions seeped into public view in February, when McMaster said at a security conference in Munich that the evidence of Russian interference in the 2016 presidential election was beyond dispute. The statement drew a swift rebuke from the president, who vented his anger on Twitter.
Trump selected McMaster last February after pushing out Michael T. Flynn, his first national security adviser, for not being forthright about a conversation with Russia’s ambassador at the time. Flynn has since pleaded guilty of making a false statement to the FBI and is cooperating with Robert Mueller, the special counsel investigating Russia’s interference in the 2016 election.
Last summer, Trump balked at a plan McMaster presented to bolster the presence of US forces in Afghanistan, although the president ultimately embraced a strategy that would require thousands more American troops.
McMaster had been among the most hard-line administration officials in his approach to North Korea, raising the specter of a “preventive war” against the North. He was among those who expressed concerns about Trump’s abrupt decision this month to meet Kim, according to a senior official.
Material from the Washington Post and the Associated Press was used in this report.