John Bolton faces a baptism of fire on Monday, his first official day as President Donald Trump's national security adviser.
The brutal chemical weapons attack in Syria presents Bolton with an immediate crisis that will highlight the biggest questions surrounding his appointment, offering an early examination of how his vision of the robust use of US power abroad will ally with Trump's own hawkish instincts.
It's a defining moment for this White House because the attack is not just a humanitarian horror, but also challenges Trump's global credibility after he fired missiles to punish President Bashar al-Assad for earlier outrages a year ago.
The frenetic, emotional hours when revulsion over a tragedy abroad turns to talk of a military response define the job of national security adviser. He or she must quickly establish facts and shape action options for a President, make him aware of the pitfalls of any decision, tease a strategy from competing military, intelligence and civilian centers of the national security establishment, and then press them to implement a presidential directive.
The Syria attack, which reportedly killed 70 people, will also test Bolton's capacity to forge trust with the commander-in-chief himself, putting their relationship - which will be crucial to his prospects - under pressure in a life-or-death environment.
And it will represent a high-pressure examination of Bolton's management style that alienated colleagues when he served as a senior State Department non-proliferation official and UN ambassador.
Bolton was planning for his new job long before the news from Syria made his first few days in office even more significant.
Contrary to many expectations, he does not plan to charge into the West Wing on a firing spree. He is likely instead to sample the temperature of the administration with a methodical approach.
Defying his reputation for turbulence and outspokenness, Bolton slipped into the White House without ceremony, in a long coat and carrying an umbrella early on Saturday morning, two days ahead of his official start date, and then tweeted a picture of him with his predecessor H.R. McMaster, whom he hailed as a patriot.
One former senior Bolton aide said the new national security adviser's goal is not to advance his personal agenda but to win Trump's trust.
"He is the President's adviser. He works for President Trump. He is going to do what President Trump tells him to do. He's going to implement the policies that President Trump wants implemented," the former aide said.
"Most importantly, he is going to do something that President Trump hasn't been getting, he is going to get a full set of well thought out policy options. The President is frustrated that he has not been getting that."
Even now, Bolton is likely to be drawing up plans for potential military action in Syria and he will preside over a principals meeting of top administration officials on Syria on Monday in order to present options to the President, two administration officials told CNN.
Early signs are that Trump wants to act, as he tweeted Sunday about the "mindless" attack, unusually criticizing Russian President Vladimir Putin for supporting "Animal" Assad and warned of a "big price" to pay.
But the Syria attack also highlights inconsistencies at the heart of Trump's foreign policy that Bolton must confront: While the President is hinting at using military force, he has recently fulminated about getting out of Syria and leaving it to regional powers to sort out.
Bigger challenges also lie in wait for Bolton, including a super power confrontation with China, a deadline on the Iran nuclear deal and Trump's summit with North Korea's Kim Jong Un.
Bolton's critics saw his appointment as the arrival of a bull in a china shop strewn with geopolitical crockery already shattered by Trump. They fear that he will not quell the President's wilder impulses - as ousted Secretary of State Rex Tillerson and McMaster tried to do - but will egg him on and lead the United States into dangerous global confrontations. Alongside Trump's nominee for secretary of state, Mike Pompeo, he is seen as part of a potential war cabinet that could enact the President's most hawkish instincts.
"I don't expect him to be a very tempering influence," said Matthew Waxman, who saw Bolton up close as a staffer on President George W. Bush's National Security Council.
"I would describe him as being extremely hawkish, especially with regard to military instruments, but also coldly calculating and rational. He is sort of like Dick Cheney in a lot of ways."
Like the former vice president, Bolton is sharply conservative. He has mooted military action against Iran and North Korea, is skeptical of negotiations with what he sees as rogue states, and has left a trail of stories about his brusque management style that infuriated past colleagues.
He's also been accused of manipulating intelligence - a charge his supporters say is unfair - and still defends the Iraq War. His failure to win Senate confirmation as President George W. Bush's UN envoy came after he was painted as a bully who victimized opponents in the intelligence community.
One critic, Carl Ford Jr., a former assistant secretary of state for intelligence and research, called him a "kiss-up, kick-down sort of guy."
Yet the image of Bolton as a mustachioed war monger does not do him justice or get at the most intriguing issues raised by his appointment.
"He has been dismissed as an ideologue, as someone reflexively, almost emotionally reacting to world events with a very narrow menu of responses," said Peter Feaver, who, like Bolton, is a former Bush national security official. "That is a gross distortion. That is unfair to him. Some of the reaction gives you the impression that he is the proverbial 3-year-old with a hammer who sees everything in the world as a nail. That is not true."
Still, Bolton's traditional skepticism about the potential of diplomacy with America's enemies could short-circuit efforts to resolve disputes peacefully and lead the United States towards more escalatory steps in foreign policy crises.
"When you are dealing with what used to be called 'pariah regimes,' he will quickly eviscerate the the more optimistic policy proposals that presume on the other side's willingness to accept win-win solutions," Feaver said.
"He will point out the flaws with those, which ends you up at the last-resort node of the decision tree. That is how he ends up being a hawk. He is not a use-force-first guy."
But Bolton's scorn for the bureaucracy of global institutions like the United Nations does not mean he spurns all diplomacy and working with allies.
He is, for example, the author of the Proliferation Security Initiative, a multilateral effort to stop the trafficking of weapons of mass destruction and their components which is universally regarded as a foreign policy success - and could be a model for US enforcement actions short of war if the North Korea summit fails.
Even Bolton's critics talk about his work ethic, intellect and depth of knowledge culled by ravenous reading of intelligence and newspapers and a mastery of the Washington Game of Thrones that makes him a more substantial figure than the blustery Fox News commentator he has become.
Christopher Hill, the Bush administration's former top North Korea negotiator, who experienced Bolton's willingness to undercut policy of an administration in which he served, called him a "relentless bureaucratic brawler."
One of the biggest questions about Bolton is how someone as expert as he is at pulling levers of a conventional administration will fare in the make-it-up-as-you-go-along chaos of the Trump presidency.
His renowned intolerance for those who lack his experience and knowledge also makes his relationship with Jared Kushner, the President's son-in-law and roving foreign policy fixer, worth watching.
And Bolton's determination to ally with the President closely could be challenged in some areas - on the potential of a North Korea summit or with Trump's determination to improve ties with Russia.
But Bolton told Fox News after his appointment that his past statements were behind him. His camp dismisses the possibility that a gulf could open between he and the President on crucial issues.
"There is no daylight between the President and Mr. Bolton on national security issues. He is a team player," the former senior Bolton aide said.