Earlier this year, as Donald Trump prepared to meet the North Korean Supreme Leader, Kim Jong Un, in Vietnam, he took a moment in the State of the Union address to congratulate himself on a diplomatic masterstroke: “If I had not been elected President of the United States, we would right now, in my opinion, be in a major war with North Korea, with potentially millions of people killed.” For John Bolton, the national-security adviser, the summit represented a conundrum. Two months before he entered the White House, in April, 2018, he had called for preëmptive war with North Korea. During the past two decades, Bolton has established himself as the Republican Party’s most militant foreign-policy thinker—an advocate of aggressive force who ridicules anyone who disagrees. In an op-ed in the Wall Street Journal, he argued that Kim’s regime would soon be able to strike the United States with nuclear weapons, and that we should attack before it was too late. “The threat is imminent,” he wrote. “It is perfectly legitimate for the United States to respond to the current ‘necessity’ posed by North Korea’s nuclear weapons by striking first.”

Trump—erratic, impulsive, and largely ignorant of foreign affairs—has promised since the start of his Presidency to scale back America’s foreign commitments and to cut its expenses. With North Korea, he began by trying to intimidate Kim into surrendering his nuclear arsenal, threatening “fire and fury” and mocking him as “Little Rocket Man.” When that failed, Trump embarked on a campaign of diplomacy by sentiment, meeting Kim in Singapore and, despite their failure to reach an agreement, declaring, “We fell in love.” In Hanoi, he intended to try again.  ……

In May, 2001, Bolton was named Under-Secretary of State for Arms Control and International Security Affairs. The terror attacks of September 11, 2001, came a few months later, and the State Department and the White House were often in conflict about how to react: Dick Cheney, the Vice-President, urged an assertive use of military power abroad, while Colin Powell, the Secretary of State, was more restrained. Lawrence Wilkerson, Powell’s chief of staff, told me that Bolton was appointed to his position only at Cheney’s insistence. “Everyone knew that Bolton was Cheney’s spy,” Mark Groombridge, an aide to Bolton at the time, told me.

George W. Bush’s Administration had vowed to attack any “rogue nation” that developed weapons of mass destruction, and Bolton began a public crusade against America’s enemies, real and presumed. In May, 2002, he spoke at the Heritage Foundation, where he accused the Cuban government of developing an ambitious biological-weapons program and of collaborating with such pariah states as Libya and Iran. As he prepared to give similar testimony to Congress, Christian Westermann, an analyst at the State Department’s internal intelligence bureau, told him that the bureau’s information did not support such a view. (Westermann declined to comment for this story.) Bolton, according to several officials, threatened to fire him. “He got very red in the face and shaking his finger at me, and explained to me that I was acting way beyond my position for someone who worked for him,” Westermann later testified. “I told him I didn’t work for him.” Bolton began excluding Westermann’s supervisor from daily briefings and, after an unsuccessful attempt to fire him, tried to transfer him to another office.

Carl Ford, who oversaw the intelligence bureau, complained to Powell that Bolton was misrepresenting the views of its officials. Powell decided to have Ford brief Congress in Bolton’s place. Bolton was angry enough that he didn’t speak to Ford for six months. Then, as Ford was preparing to retire, Bolton called him on the phone. “He told me he was glad I was leaving,” Ford said. (Bolton denies making this call.)

Bolton’s immersion in the arcana of weapons of mass destruction encouraged an absolutist view. “The first thing he thinks about in the morning is protecting Americans from nuclear weapons,” Sarah Tinsley, who has worked as an aide to Bolton since the eighties, told me. In 2003, as he prepared testimony for an appearance before Congress, he described Syria’s efforts to produce nuclear and biological weapons as an urgent threat—an assessment that intelligence agencies thought was exaggerated. A bitter internal debate ensued; the accusations endangered the Syrian government’s coöperation in hunting suspected terrorists. “We were getting some of our best, if not our best, intelligence on Al Qaeda from Damascus,” Lawrence Wilkerson told me. Richard Armitage, the Deputy Secretary of State, took Bolton aside and “told him to shut up,” Wilkerson said. Before Bolton testified to Congress, much of his language was diluted. Armitage reached out to a team of intelligence officers who vetted public statements made by State Department officials, and asked them to give special scrutiny to Bolton’s. “Nothing Bolton said could leave the building until I O.K.’d it,” Thomas Fingar, who led the team at the time, told me.