Jared Kushner, President Donald Trump’s principal Middle East advisor, embarked on his maiden diplomatic mission even before his father-in-law was inaugurated. His task: get Britain to help scuttle a U.N. Security Council resolution denouncing Israeli settlements.

His outreach was part of a broader effort by the president-elect’s transition team — which included public denunciations of the settlements resolution by Trump, and back-channel lobbying of U.N. diplomats by his not-yet-then-and-now-former national security advisor, Michael Flynn, to derail the resolution vote. It ultimately failed, as the council’s 15 members, including Britain, dismissed the Trump team’s appeals and voted 14-0, with a U.S. abstention, in favor.

But Kushner’s intervention provided an early test of the neophyte’s attempt to wade into a Middle East morass that has bedeviled professional diplomats for decades. It also provided further insights into a rare effort by an incoming administration to press America’s closest ally to break ranks with a sitting American president.

Shortly before the Dec. 23 vote on Israeli settlements, and full month before Trump would take office, Kushner contacted Kim Darroch, Britain’s ambassador to the United States, who he had met through a friend. Kushner asked Darroch to push back the vote on the resolution until after the inauguration, a White House official told Foreign Policy, a move that would give the new administration the chance to veto it. Kushner argued that the resolution would ease the pressure on the Palestinians to enter peace talks with Israel.

It was a particularly big ask for Britain, which had been pressing for the council to weigh in on the Middle East crisis since 2014. Britain’s U.N. ambassador, Matthew Rycroft, played a decisive, behind-the-scenes role in helping draft a resolution that could avoid an American veto.

Britain rebuffed Kushner’s appeal. After the vote, Rycroft defended Britain’s action, saying, “Israeli settlement activity represents a clear and present danger to our shared vision of two states for two people.”

The vote triggered a furious response from the Trump transition team that caught Britain’s foreign-policy establishment — as well as the country’s new prime minister, Theresa May — off balance.

President-elect Trump denounced the resolution in a statement, calling it “extremely unfair to all Israelis.” Reinforcing the point on Twitter, he warned that “things will be different” at the U.N. after his Jan. 20 inauguration.

Kushner, meanwhile, went to work on the British, applying intense pressure on Darroch to shift gears and align his government’s policy more closely with the incoming administration. It would pay off in less than a week, when May in a speech eviscerated then-Secretary of State John Kerry over Israel.

“He gave the Brits a tough time because of their vote on the settlements resolution,” said a senior Western diplomat.

Asked if Kushner had read British officials the riot act, a White House official said it was “hard to imagine” the normally reserved man delivering a smackdown. But “he was very disappointed,” the official said.

Obama administration officials viewed the Trump administration’s efforts to block the settlements resolution as a flagrant breach of diplomatic protocol and a violation of the tradition of having one president at a time.

American officials in New York and Washington soon began to notice that Britain was becoming an obstacle on other fronts, delaying action on a U.S.-backed resolution threatening sanctions against Syria for using chemical weapons.

“This was starting to happen more and more,” recalled one former senior U.S. official, who claimed the British were coordinating with Trump’s team. “It was a strange experience, it was quite unusual during an American transition to have close allies blatantly tell you they need to consult with the new administration.”

May’s government was in a tough spot. With Britain poised to leave Europe, she was keen to shore up the “special relationship” — a centerpiece of British foreign policy since World War II — with the incoming administration and secure an early meeting with President Trump. In mid-December, more than a month before the inauguration, her chiefs of staff, Fiona Hill and Nick Timothy, traveled to New York to meet with Trump’s advisors.

“All it took was one phone call” from Kushner to convince the British to take a tougher line, said a senior European source.

May moved quickly to mollify Trump well before he took office, breaking ranks with the outgoing Obama administration, not to mention Britain’s own European allies, on a range of Middle East fronts.

On Dec. 30, May delivered an extraordinary rebuke of Secretary Kerry. He had called Prime Minister Benjamin Netanyahu’s government the “most right-wing” in the country’s history and warned that Israel’s settlement policy was undermining any prospects for the establishment of a Palestinian state.

“We do not believe that it is appropriate to attack the composition of the democratically elected government of an ally,” May retorted.

The remarks rattled some British diplomats.

“The language was aggressive, and people were taken aback. It was not how the Foreign Office would have phrased things,” said a former senior British diplomat.

But it was not enough to satisfy the incoming administration.

Kushner was said to be simmering over May’s remarks, which failed to fundamentally alter London’s views on the virtues of the settlements resolution. One diplomat suggested the statement may not have put enough daylight between Britain and the Obama administration. “Or maybe he’s just always angry,” the diplomat said.

Britain’s foreign secretary, Boris Johnson, paid a Jan. 8 visit to Trump Tower, the president-elect’s residence and transition headquarters in New York, to smooth things over with Kushner and Steve Bannon.

Trump’s advisors were alarmed by French plans to host a high-level Middle East meeting the next week in Paris, which would have reinforced international opposition to settlements. Johnson declined to go to Paris, sending a lower level British official in his place. British officials subsequently blocked the adoption of European Union statements in Brussels and the U.N. Security Council endorsing the Paris communique, which had reinforced international denunciation of Israel’s settlements.

Thomas Barrack Jr., a Lebanese-American fundraiser and advisor to Trump, praised Kushner’s role in trying to block the settlements resolution. His “instinct of sensing a moment in time in which this president might put his fingerprints on a peaceful solution to decades-old issues was timely and appropriate,” he said.

Meanwhile, one critic dismissed Kushner’s apparent achievement in getting the British to break with the Obama administration as a “maiden mini-success.”

“It was almost inevitable that Theresa May, given her agenda, her priorities, and her domestic political situation, would both have to and want to run to embrace Trump,” said Hussein Ibish, a senior resident scholar at the Arab Gulf States Institute in Washington.

“So, in a sense, getting May to make Trump- and Israel-friendly noises was not hard at all. There was almost no way to fail. I think anyone could have done it,” he said.

Obama administration officials, still in office, were irate. For several months, Britain and France had been pressing the United States to join them in presenting a U.N. Security Council resolution sanctioning Syria and the Islamic State for using chemical weapons. Russia had made it clear it would veto the resolution, but for the two Europeans allies it was worth exposing Russia’s defense of the Syrian regime.

The United States initially balked, fearing a confrontation with Russia might jeopardize Kerry’s efforts to negotiate with Moscow a cease-fire in eastern Aleppo. But by December, Aleppo had already fallen, and the Obama administration began pressing for a vote on the chemical weapons resolution. But when they went back to the British, they got a cold shoulder.

“I felt like I got the runaround,” said the official. “I took it to mean the Obama administration was out of juice.”

At the same time, the British began to backtrack on another joint initiative with the Obama administration. In December, the Obama administration urged Spain, which held the rotating council presidency, to schedule a meeting with Ismail Ould Cheikh Ahmed, the U.N. special representative on Yemen. The Spanish declined.

When Sweden took up the presidency in January, the British held up scheduling the meeting until three days after Trump’s inauguration.

“They were less than subtle about needing to check with the incoming team,” said a former U.S. official.

“They were just waiting us out,” said another former U.S. official.

But in the end, for all the cajoling, Kushner and his colleagues had done little to shake Britain’s position on Israeli settlements.

The episode underscored the limits of the Trump presidency’s power to impose its vision of the Middle East on even its closest allies.

In her first Security Council meeting on the Middle East, Nikki Haley, the new U.S. ambassador to the United Nations, was still fuming over what she characterized as the “outrageously biased” settlements resolution passed by the council in December.

But Britain’s U.N. ambassador punched back, making it clear that London had no regrets.

“I don’t think the Security Council is biased against any country; we are biased in favor of the U.N. charter,” Rycroft said. “We oppose any country or any action that goes against the U.N. charter.”

The settlements resolution, he added, was “neither pro nor anti any country. It was anti-settlements, on the grounds that settlements are one of the impediments to bringing peace to the Middle East.”

FP‘s senior national security reporter Dan De Luce contributed to this story.