As a cheerleader for Brexit, Boris Johnson played a key role in selling Britons on the miraculous benefits of leaving the EU. Now, as the U.K.’s new prime minister, he’ll be asked to actually deliver them.

Johnson, the divisive former Foreign Secretary, was named as Theresa May’s replacement Tuesday, following a seven-week contest in which 160,000 members of the ruling Conservative party whittled down the candidates from 10 to one. As expected, Johnson prevailed over his sole remaining rival, Jeremy Hunt, by a convincing margin, winning 66% of the vote.

In a typically jovial acceptance speech that would have sounded alarm bells to his many detractors — who feel his jokey demeanor masks a fundamental lack of seriousness and unfitness to lead — Johnson acknowledged the widespread reservations about his victory. Even some of his backers, he noted, might “wonder quite what they have done.”

But he struck an optimistic note as he addressed the steep challenges he will face when he inherits a government three years deep into the seemingly unsolvable Brexit debacle.

“I read in my Financial Times this morning … that no incoming leader has ever faced such a daunting set of circumstances,” he said. “Well, I look at you this morning and ask: ‘Do you look daunted?’ I don’t think you look remotely daunted. I think we can do it and I think the people of this country are trusting in us to do it and we know that we will do it.”

Johnson, 55, is the charismatic former mayor of London and a product of the British elite, and has long coveted the role of prime minister. He was a favorite to succeed former leader David Cameron when Cameron stepped down in the wake of the 2016 EU referendum. But Johnson’s leadership bid faltered unexpectedly when key backers in the party shifted their allegiances, and picked May instead.

Starting Wednesday, he’ll finally step into the top job, taking the reins of power amid a roiling political crisis over Brexit — a situation he played a decisive role in creating.

In 2016, despite pressure from then-leader Cameron to join him in backing the Remain campaign, Johnson broke ranks to become one of the most prominent advocates for Brexit. Many critics saw the move as a reflection of his craven appetite for power rather than any underlying ideological conviction.

But three years on, Brexit still hasn’t happened. Britain remains deeply divided, locked in a damaging stalemate over the greatest political crisis to face the country in decades. May failed repeatedly to get the exit deal she negotiated with the EU passed by her Parliament, and it ultimately cost her her premiership.

By contrast, Johnson has vowed that, as prime minister, he will be prepared to lead the country to a “no deal” Brexit in October if the EU doesn’t cut Britain a new deal. Credit rating agencies and the government’s own spending watchdog have warned that leaving the EU in this way will seriously damage the British economy.

Johnson’s threats have sent the value of the pound plummeting and triggered a rash of resignations from Cabinet. Foreign Office Minister Sir Alan Duncan and Education Minister Anne Milton both resigned this week in protest of a potential Johnson victory, while three other cabinet ministers – Philip Hammond, Rory Stewart and David Gauke – said they would resign from cabinet rather than serve under Johnson, because of his threats of a no-deal Brexit.

Johnson, a former journalist who made his name with stories that railed against the European Union, was Mayor of London from 2008 to 2016. He developed a popular personal brand among voters, thanks to his unkempt, bumbling, and sometimes buffoonish public image.

But for many, his charm has worn thin in recent years. Beyond his association with the false promises of the Leave campaign — among them, that Brexit would leave the beleaguered National Health Service with an additional £350 million a week — Johnson’s distracted, lackluster performance as Foreign Secretary, and scandals in his private life, have fueled concerns about his fitness to lead.

His shambolic performance as foreign secretary included inaccurate public comments that a British-Iranian woman being held in an Iranian jail on charges of espionage had been teaching journalism — remarks that Iran’s regime used as a justification for her ongoing detention. He also drew criticism in 2017 after it emerged he had recited a colonial-era Rudyard Kipling poem in front of local dignitaries during a visit to a sacred Buddhist temple in Myanmar.

He’s also been criticized for repeated episodes of casual racism, writing in a newspaper column in August last year that Muslim women who wore niqabs or burqas look like letterboxes or bankrobbers. In another column in 2002, he referred to children in the British Commonwealth as “flag-waving piccaninnies” and described people in the Congo as having “watermelon smiles.”

Jeremy Corbyn, leader of the opposition Labour Party, was quick to attack Johnson after his victory was announced Tuesday, pointing out that he had become prime minister through a race decided on by members of the Conservative Party, rather than contesting a general election.

“Johnson has won the support of fewer than 100,000 unrepresentative Conservative Party members by promising tax cuts for the richest, presenting himself as the bankers' friend, and pushing for a damaging No Deal Brexit,” he tweeted. “But he hasn't won the support of our country… The people of our country should decide who becomes the Prime Minister in a General Election.”

Scotland's First Minister Nicola Sturgeon, the leader of her country’s devolved parliament, was also quick to voice skepticism about Johnson’s win, saying she had deep misgivings about his leadership.

“I have profound concerns about the prospect of his premiership and it would be hypocritical not to be frank about these,” said Sturgeon, whose country voted in favor of remaining in the EU in the 2016 referendum, but will be forced to leave due to the overall British majority in favor of Brexit.

“These are concerns that I am certain will be shared by the vast majority of people in Scotland who, had they been given any say, would not have chosen to hand the keys of Number 10 to someone with his views and track record.”

Labour MP David Lammy said Johnson’s victory was a “sad indictment” of the class system’s enduring grip on modern Britain. “Even after a career marked by incompetence, lies and vanity, if you have been to the right school and university, you can get the top job in the country,” he tweeted.

But Johnson also has powerful admirers, not least among them President Donald Trump. Johnson had harsh words for Trump before either of them came to power — in 2015, Johnson said Trump’s campaign-trail remarks about supposed Muslim no-go zones in the British capital displayed “a quite stupefying ignorance that makes him, frankly, unfit to hold the office of president.”

But the U.S. leader was among the public figures to congratulate the incoming British PM, who is often compared to Trump for his populist politics, freewheeling public speaking style, and flexible relationship with the truth.

“He will be great!” Trump tweeted.