Senior US officials were worried. Since the early months of the Trump administration, Jared Kushner, the president’s son-in-law and Middle East adviser, had been having private, informal conversations with Prince Mohammed bin Salman, the favourite son of Saudi Arabia’s king.

Given Mr Kushner’s political inexperience, the private exchanges could make him susceptible to Saudi manipulation, said three former senior US officials. In an effort to tighten practices at the White House, a new chief of staff tried to re-impose long-standing procedures stipulating National Security Council staff members should participate in all calls with foreign leaders.

But even with the restrictions in place, Mr Kushner, 37, and Crown Prince Mohammed, 33, kept chatting, according to three former White House officials and two others briefed by the Saudi royal court. In fact, they said, the two men were on a first-name basis, calling each other Jared and Mohammed in text messages and phone calls.

The exchanges continued even after the 2 October killing of Jamal Khashoggi, the Saudi journalist who was ambushed and dismembered by Saudi agents, according to two former senior US officials and the two people briefed by the Saudis.

As the killing set off a firestorm around the world and US intelligence agencies concluded it was ordered by Crown Prince Mohammed, Mr Kushner became the prince’s most important defender inside the White House, people familiar with its internal deliberations say.

Mr Kushner’s support for Crown Prince Mohammed in the moment of crisis is a striking demonstration of a singular bond that has helped draw President Donald Trump into an embrace of Saudi Arabia as one of his most important international allies.

But the ties between Mr Kushner and Crown Prince Mohammed did not happen on their own. The crown prince and his advisers, eager to enlist US support for his hawkish policies in the region and for his own consolidation of power, cultivated the relationship with Mr Kushner for more than two years, according to documents, emails and text messages reviewed by The New York Times.

A delegation of Saudis close to the crown prince visited the United States as early as the month Mr Trump was elected, the documents show, and brought back a report identifying Mr Kushner as a crucial focal point in the courtship of the new administration. He brought to the job scant knowledge about the region, a transactional mind-set and an intense focus on reaching a deal with the Palestinians that met Israel’s demands, the delegation noted.

Even then, before the inauguration, the Saudis were trying to position themselves as essential allies who could help the Trump administration fulfil its campaign pledges. In addition to offering to help resolve the dispute between Israel and the Palestinians, the Saudis offered hundreds of billions of dollars in deals to buy US weapons and invest in US infrastructure. Mr Trump later announced versions of some of these items with great fanfare when he made his first foreign trip: to an Arab-Islamic summit in Riyadh, the Saudi capital. The Saudis had extended that invitation during the delegation’s November 2016 visit.

“The inner circle is predominantly deal-makers who lack familiarity with political customs and deep institutions, and they support Jared Kushner,” the Saudi delegation wrote of the incoming administration in a slide presentation obtained by the Lebanese newspaper Al Akhbar, which provided it to The Times. Several Americans who spoke with the delegation confirmed the slide presentation’s accounts of the discussions.

The courtship of Mr Kushner appears to have worked.

Only a few months after Mr Trump moved into the White House, Mr Kushner was enquiring about the Saudi royal succession process and whether the United States could influence it, raising fears among senior officials that he sought to help Crown Prince Mohammed, who was not yet the crown prince, vault ahead in the line for the throne, two former senior White House officials said. US diplomats and intelligence officials feared the Trump administration might be seen as playing favourites in the delicate internal politics of the Saudi royal family, the officials said.

By March, Mr Kushner helped usher Crown Prince Mohammed into a formal lunch with Mr Trump in a state dining room at the White House, capitalising on a last-minute cancellation by Chancellor Angela Merkel of Germany because of a snowstorm.

“The relationship between Jared Kushner and Mohammed bin Salman constitutes the foundation of the Trump policy not just towards Saudi Arabia but towards the region,” said Martin Indyk, a fellow at the Council on Foreign Relations and a former Middle East envoy. The administration’s reliance on the Saudis in the peace process, its support for the kingdom’s feud with Qatar, a US ally, and its backing of the Saudi-led intervention in Yemen, he said, all grew out of “that bromance.”

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‘You will love him’

Before the 2016 presidential race, Mr Kushner’s most extensive exposure to the Middle East was through Israel. Prime Minister Benjamin Netanyahu was a Kushner family friend, and the Kushners had contributed heavily to Israeli non-profits supporting Jewish settlements in the Palestinian territories of the West Bank.

But the Arab rulers of the oil-rich Persian Gulf mainly figured in Mr Kushner’s life as investors in US real estate, the Kushner family business.

So Tom Barrack, a Lebanese-American real estate investor with close ties to both Mr Trump and the Gulf rulers, set out during the campaign to introduce Mr Kushner to his associates as a useful ally.

“You will love him and he agrees with our agenda!” Mr Barrack wrote in May 2016 in an email to the Emirati ambassador in Washington, Youssef Otaiba.

‘Lack of familiarity’ with history

Top aides to Saudi Arabia’s Crown Prince Mohammed also met with Mr Kushner on a trip to New York in November 2016, after the election.

The Saudi team included Musaad al-Aiban, a Cabinet minister involved in economic planning and national security, and Khaled al-Falih, installed by the crown prince as minister of energy and chairman of the state oil company, according to executives who met with them and a person who was briefed on the meetings. Mr Al-Aiban did not respond to a request for comment and Mr al-Falih could not be reached for comment.

The delegation made special note of what it characterised as Mr Kushner’s ignorance of Saudi Arabia.

“Kushner made clear his lack of familiarity with the history of Saudi-American relations and he asked about its support for terrorism,” the team noted in the slide presentation prepared for Riyadh. “After the discussion, he expressed his satisfaction with what was explained about the Saudi role in fighting terrorism” and what the Saudis said was their international leadership in fighting Islamist extremism.

Mr Kushner, the Saudi report said, also questioned the delegation’s motives, asking whether the group had always been interested in working with Mr Trump. As a candidate, Mr Trump had promised to ban Muslim immigrants from entering the United States and had singled out Saudi Arabia as a dangerous influence.

“Kushner wondered about Saudi Arabia’s desire for partnership and whether it came from opportunity or worry, and he wondered as well if it was specific to this US administration or whether it was presented to Hillary Clinton (for example: women driving),” read another slide, next to a photograph of Mr Kushner.

But Mr Kushner was clear about his own priorities, the report said. “The Israeli-Palestinian conflict was among the most important issues to draw Kushner’s attention,” the delegation reported, and therefore the best way to win him over.

“The Palestinian issue first: there is still no clear plan for the American administration towards the Middle East,” the delegation wrote, “except that the central interest is finding a historic solution to support the stability of Israel and solve the Israeli-Palestinian conflict.”

To cultivate ties with the Trump team, the Saudis had prepared a long list of initiatives they said would help Mr Trump deliver for his supporters.

Seizing on Mr Trump’s campaign vows for the “extreme vetting” of immigrants, the Saudi delegation proposed “establishing an intelligence and data” exchange “to help the American administration carry out its strategy of investigating those requesting residency (extreme vetting),” according to an Arabic version of a presentation for the Trump team.

And the delegation pledged “high-level coordination with the new American administration” to help with “defeating extremist thought.”

Several of the Saudi proposals were evidently welcomed.

One was a “joint centre to fight the ideology of extremism and terrorism.” Mr Trump helped inaugurate a Saudi version of the centre on his trip to Riyadh the following May.

Donald Trump defends Saudi Arabia accusation of Jamal Khashoggi murder: 'Do people really want me to give up hundreds of thousands of jobs?'

Another Saudi proposal outlined what the Trump administration later called “an Arab NATO.” In their presentation, the Saudis described it as an Islamic military coalition of tens of thousands of troops “ready when the president-elect wishes to deploy them.”

Other initiatives appeared timed to Mr Trump’s first term in office, like proposals to spend $50 billion over four years on US defence contracts, to increase Saudi investment in the United States to $200 billion over four years, and to invest, with other Gulf states, up to $100 billion in American infrastructure.

And the delegation urged Mr Trump to come to Saudi Arabia himself to “launch the initiatives as part of a historic welcome celebration.”

A Saudi role in Middle East Peace

Israel had long argued to US diplomats that Saudi Arabia’s influence in the region made it essential to any peace deal, and the Israelis were developing high hopes for Crown Prince Mohammed because of his hawkish views towards Iran and his general iconoclasm (he would later make several statements, like affirming the Israeli “right” to land, that were notably more sympathetic to the Israeli position than those of other Saudi leaders.)

Within weeks of Mr Trump’s move into the White House, Mr Kushner had embraced the delegation’s proposal for the president to visit Riyadh, convinced by then that the alliance with Saudi Arabia would be crucial in his plans for the region, according to a person who discussed it with Mr Kushner and a second person familiar with his plans.

The secretary of state at the time, Rex Tillerson, opposed the idea. It would link the administration too closely to Riyadh, these people said, giving up flexibility and leverage. Mr Trump initially saw little benefit either, according to a person involved in his deliberations.

But by the time of the inauguration, Mr Kushner was already arguing that under the influence of Crown Prince Mohammed, Saudi Arabia could play a pivotal role in advancing a Middle East peace deal, according to three people familiar with his thinking. That would be the president’s legacy, Mr Kushner argued, according to a person involved in the discussions.

It was around the time of the White House visit in March 2017 that senior officials in the State Department and the Pentagon began to worry about the one-on-one communications between Crown Prince Mohammed — who is known to favour the online messaging service WhatsApp — and Mr Kushner. “There was a risk the Saudis were playing him,” one former White House official said, speaking on the condition of anonymity to discuss internal deliberations.

One former White House official argued Mr Kushner’s personal ties to Crown Prince Mohammed had sometimes been an asset. At one point, for example, the Saudi-led coalition fighting in Yemen had blocked a critical port, cutting off humanitarian and medical supplies. The national security adviser at the time, Lt General HR McMaster, suggested Mr Kushner call Crown Prince Mohammed to address the issue, the official said, and Mr McMaster believed Mr Kushner’s intercession had helped persuade the Saudis to loosen the restrictions.

Inside the White House, Mr Kushner has continued to argue that the president needs to stand by Crown Prince Mohammed because he remains essential to the administration’s broader Middle East strategy, according to people familiar with the deliberations.

Whether Crown Prince Mohammed can fulfil that role, however, remains to be seen. His initial approaches to the Palestinians were rejected by their leaders, and their resistance stiffened after the Trump administration recognised Jerusalem as Israel’s capital without waiting for a negotiated agreement on the city’s status.

Now the crown prince’s father, King Salman, 82, who is still the official head of state, has appeared to resist Mr Kushner’s Middle East peace plans as well.

“The Palestinian issue will remain our primary issue,” the king declared in a speech last month, “until the Palestinian people receive all of their legal rights.”