All he had to do was keep smiling and let the extravagant hospitality of his Saudi hosts carry him through the day, which reached a high point with the signing of the biggest arms deal in history.

There's nothing like an investment of $110bn (£85bn) with the prospect of a further $250bn (£192bn) in trade to settle the stomach after a queasy few weeks back home.

It's unlikely that King Salman would have asked about why Donald Trump fired James Comey, boasted about it to the Russians or what he thought his odds were in beating calls for the President's impeachment.

Mr Trump, we can be sure because the deal was done, probably didn't bring up Saudi Arabia's human rights record, the absence of a free press, or the campaign in the Yemen against Shia rebels which has been criticised for high levels of civilian casualties.

When you're looking to reset the directions of diplomacy with a new map and in a vehicle lubricated with billions of petrodollars, it doesn't do to tip the sands of awkward truth into the gearbox.


Trump waves blade in Saudi sword dance

So there has been no mention of Mr Trump's near innumerable attacks on the Muslim faith, best summed up with his line from the presidential campaign: "Islam hates us."

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The Saudis have focused on trying to get across that it is only a perverted version of their faith that leads to violence, and that they are in the forefront of fighting it - literally in Syria and Iraq and virtually, through a global digital hub, that Mr Trump will open in Riyadh.

This is all fine.

But on his second day in the kingdom, Mr Trump is due to address the combined heads of state and government of some 30 predominantly Muslim countries.

Before he left, he told Americans in a TV address that he expected the Islamic world to do more to fight extremism. Many of the leaders may agree with him.

Saudi king greets Trump in Riyadh

Addressing the roots of Islamic extremist terror takes more than asking Muslims to do some soul searching.

Osama bin Laden, the late founder of al Qaeda, was viciously extreme in his hatred of the West. But his following did not expand beyond a few dozen veterans of the Afghan war against the Soviets until his successful plot to attack America on 9/11.

He hoped to provoke an unequal and opposite reaction - and he got it. Within three years, the West was at war in two major Islamic nations, Afghanistan and Iraq, where chaos and bloodshed have reigned now for more than a generation - spreading into Syria and elsewhere.

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Image: Mr Trump's campaign stance on Islam would alienate his audience in Saudi Arabia

Dr Hamid el Shaygee is a leading sociologist at the Mohammed bin Nayef Centre, which has pioneered the de-radicalisation of violent Islamists.

He insisted that often they asked themselves the right questions - such as "why has the West attacked Muslim nations?" - but "come up with the wrong answer": that violence is a "rational and religious response".

This, though, is old hat to the Sunnis of the Middle East. They know they're facing the scourge of violent nihilism and the Islamic State's death cult. Right or wrong, they believe they'll prevail.

Winning the war against extremism and ending the clash of civilisations bin Laden so deliberated engineered requires an increasingly subtle campaign waged in the cybersphere, on the ground, and in the realms of theology and philosophy.

Mr Trump will have to travel a long way from "Islam hates us" to win over his audience on day two of his Saudi sojourn.