A key player in the US-Saudi relationship is conspicuously missing from the talks held in Riyadh by the US secretary of state, Mike Pompeo, to try to defuse the international crisis over the disappearance of Jamal Khashoggi.

Jared Kushner helped build the alliance between the House of Saud and the House of Trump. The president’s son-in-law and senior adviser took the lead in promoting Mohammed bin Salman as a Saudi visionary, and persuaded the administration to hitch US Middle East policy to the prince’s rising star.

Together the two thirty-something princelings, MBS and Kushner, stayed up late into the night planning to remake the map of the Middle East with bold thinking and mountains of cash. For now, however, those plans are stalled. The Saudi crown prince stands accused of masterminding the cold-blooded murder of a dissident journalist, Kushner is silent and Donald Trump has been performing crisis public relations for the Saudi monarchy.

Peppered with questions on Monday, the president gamely suggesting that the suspected hit team that arrived in Istanbul on official jets and had free run of the Saudi consulate there, were “rogue killers” acting without the knowledge of the prince or his father, King Salman.

Pageantry and promises

The scramble for alibis is a long way from the high hopes of May last year, when the Trump–Saud courtship was consummated. The new president made Riyadh the destination of his first trip abroad since taking office. In the months before, Kushner identified MBS as a potential partner. The state department and the CIA backed Mohammed bin Nayef, the incumbent crown prince at the time, but the first son-in-law insisted that he had “reliable intelligence” – most likely from the Israeli president, Benjamin Netanyahu, a Kushner family friend – that Mohammed Bin Salman was the man to bet on. The prophecy became self-fulfilling as wholehearted support from Washington aided Mhis rise, eventually eclipsing and replacing Nayef.

Meanwhile, the Riyadh summit appeared to be a glittering success. Trump was flattered and feted, given a sword with which to dance in step with King Salman and his retinue. There was a flypast of nine warplanes, the most the Saudis had ever attempted, and horses alongside the limos.

The pageantry was backed up with substance. King Salman had gathered other Gulf Arab leaders in Riyadh to promise to fight terrorism and Iran, which both the hosts and their US guests viewed pretty much as one and the same.

Mike Pompeo (centre) greets Saudi officials on his arrival in Riyadh on Tuesday. Photograph: Leah Millis/AP

In Riyadh, Trump also claimed that he had managed to sell the Saudis $110bn (£83bn) in US-made weapons. The president cited the figure again last week to explain why he could not afford to impose sanctions on the Saudi royal family even if they were found to have murdered Khashoggi, but it was largely illusory. It included deals agreed under the Obama administration and some statements of intent to buy some weapons systems, but no actual new contracts.

However, arms sales were just part of the bonanza MBS promised Trump. When the crown prince made a three-week tour of the US in March this year, he made a point of visiting the titans of US tech industries on the west coast. The Saudi Public Investment Fund (PIF), pledged $45bn to the Japanese group SoftBank towards its planned $100bn technology venture capital fund.

PIF also bought a $3.5bn share in the ride-sharing company Uber; a $2bn stake in the electric carmaker Tesla; and put about $1bn in Virgin Group’s space companies.

US and Saudi economies entwined

It was a statement of intent. The nation built on oil wealth was buying a stake in a low-carbon future. As part of the crown prince’s Saudi Vision 2030, a futuristic megacity called Neom would rise from the sands, run by artificial intelligence and serviced by robots. It would be a huge potential market for Silicon Valley.

As the US and Saudi economies became ever more intertwined, their foreign policies lined up in parallel. The Obama administration had sought to balance Saudi Arabia and Iran but Trump would be all in alongside Riyadh against Tehran. And the Saudis would back Kushner’s big project, a peace deal between Israel and the Palestinians.

When Congress raised doubts about the kingdom’s worsening human rights record, as Bin Salman crushed dissent inside Saudi Arabia and locked up his princely rivals in the Riyadh Ritz-Carlton, or about the terrible civilian deaths from the Saudi-led coalition’s aerial bombing campaign in Yemen, there was lots of lobbying money to smooth the way.

According to the Centre for International Policy, the Saudis spent $27m on Washington lobbying firms in 2017, three times what they spent in 2016. Of that, $400,000 went straight to the campaign funds of senators and House members who were urged to turn a blind eye to Saudi excesses.

In the end, it was not the mass crackdown on dissent that slowed the Trump-Saud locomotive in its tracks, nor the deaths of thousands of civilians in Yemen. Not even the death of 40 Yemeni boys on a school outing, killed by a US-made, Saudi-dropped bomb in August, caused much of a ripple in the bilateral relationship.

The disappearance and suspected murder of one man has done more to jeopardise US-Saudi relations than three years of bombing and blockades in Yemen. Khashoggi is a US resident and a contributor to the Washington Post, whose owner, Jeff Bezos, the founder of Amazon, was one of the west coast moguls MBS schmoozed in March.

As the Saudi government has flailed in response to damning Turkish leaks about Khashoggi’s reported murder and dismemberment, lashing out at its critics and putting up a wall of denial, the procession of western businesses cutting their ties with Riyadh has become a stampede.

Jared Kushner, White House adviser and President Trump’s son-in-law, at the Saudi royal court in Riyadh. Photograph: Jonathan Ernst/Reuters

One tech and media company after another has sent its regrets to the Future Investment Initiative conference, the flagship of Bin Salman’s westernising aspirations known as “Davos in the desert”.

The Saudi regime’s staunchest remaining friend in the west is the Trump administration. As of Tuesday, the treasury secretary, Steven Mnuchin, was still planning to attend the Riyadh conference. But Trump’s loyalty to the Saudi royals is stretching his credibility to breaking point even with the Republican faithful in Congress.

Discontent in the senate

A bipartisan list of 22 senators have asked the US to carry out an investigation of what happened to Khashoggi and report back in 120 days with a decision on whether to impose sanctions on those responsible. The Senate can be expected to be sceptical about claims that “rogue killers’ were responsible.

Meanwhile, senators from both parties wrote last week to Pompeo challenging his argument for continuing to certify arms exports to Saudi Arabia and asking that he return to Congress by the end of the month to shore up his case.

Even if the Senate does vote against arms sales to Saudi Arabia, Trump could tough it out and overrule congressional disapproval with a veto. But it would mark a major rift between the president and his party.

Gerald Feierstein, a former US diplomat who was principal deputy assistant secretary of state for near-eastern affairs in the Obama administration, said: “The Senate might not stop arms sales but the symbolism of a vote of disapproval would be significant and could influence the administration to change direction.”

Few expect the House of Saud to fall over the Khashoggi affair, but the grander ambitions promoted by Bin Salman have visibly sagged and could collapse, taking with it a lot of the House of Trump’s remaining lustre.