Trump can expect a warm welcome in Saudi Arabia where he is to meet King Salman and other senior royals -- in sharp contrast to Washington where pressure is building over his team's alleged links to Moscow.
Air Force One had barely taken off when it was announced that James Comey, the former FBI chief fired by Trump, had agreed to testify publicly about Russian interference in the US elections.
Reports also emerged that Trump had called Comey "a nut job" and that the FBI had identified a senior White House official as a "significant person of interest" in its probe of Russian meddling.
A red carpet was rolled out and staircase rolled up to Air Force One after it landed at King Khalid International Airport in Riyadh shortly before 9:50 am (0650 GMT).
Trump and his wife Melania, who dressed conservatively in black but did not cover her hair, walked side-by-side to the tarmac where they both shook hands with Saudi King Salman.
Trump is to hold talks with King Salman and the kingdom's two powerful crown princes later on Saturday, before giving a speech on Islam to leaders of Muslim countries on Sunday.
For Riyadh the visit is an opportunity to rebuild ties with a key ally, which were strained under Trump's predecessor Barack Obama who Sunni Arab Gulf states suspected of a tilt towards their Shiite regional rival Iran.
That, together with a more muted focus on human rights and the likely announcement of new arms deals, should please Washington's traditional Sunni Gulf allies.
"He's going to be tougher on Iran," said Philip Gordon, senior fellow at the Council on Foreign Relations. "He's not going to lecture them on democracy and human rights."
Sunday's speech to dozens of Muslim leaders has been touted as a major event -- along the lines of a landmark address to the Islamic world given by Obama in Cairo in 2009.
The speech will be especially sensitive given tensions sparked by the Trump administration's attempted travel ban targeting several Muslim majority nations and accusations of anti-Islamic rhetoric on the campaign trail.
"I'll speak with Muslim leaders and challenge them to fight hatred and extremism, and embrace a peaceful future for their faith," Trump said ahead of his visit.
Trump wants Gulf states in particular to do more to tackle extremists such as the Islamic State jihadist group.
"He will encourage our Arab and Muslim partners to take bold, new steps to promote peace and to confront those, from ISIS to Al-Qaeda... who perpetuate chaos and violence that has inflicted so much suffering throughout the Muslim world and beyond," said Trump's National Security Adviser H.R. McMaster.
Before departing, the president tweeted he would be "strongly protecting American interests" on his marathon eight-day trip to the Middle East and Europe.
After Saudi Arabia, Trump will head to Israel and the Palestinian Territories where he hopes to revive the moribund peace process.
He then travels to Europe where he will hold face-to-face meetings including with Pope Francis and France's new leader, Emmanuel Macron.
It is a trip fraught with peril for the real estate magnate, who is known to dislike lengthy travel.
The avalanche of revelations in the run-up to his departure have eroded Trump's standing at home -- where the parallels with Richard Nixon's ill-fated presidency are now being openly drawn.
On Friday, a report by The Washington Post that the probe into his campaign's Russia ties had identified a "significant person of interest" in the White House undercut Trump's insistence his election bid had nothing to do with the Kremlin.
The White House was rocked by another bombshell when reports emerged that Trump said his firing of "nut job" Comey had relieved "great pressure" on him due to the investigation.
The scandals have revived questions about his ability to strike a presidential tone with his foreign counterparts, with Trump declaring himself the victim of the "greatest witch hunt" in American political history.
Arms contracts
His visit to the Gulf is expected to bring lucrative arms contracts for US firms.
"The big question mark that you should bear in mind is if Saudi Arabia signs up for a $100 billion arms deal with oil prices where they are today, how are they actually going to pay that in the future?" said Bruce Riedel, former CIA analyst and counterterrorism expert now with the Brookings Institution.
In Israel, Trump will meet his "friend" Israeli Prime Minister Benjamin Netanyahu in Jerusalem and Palestinian president Mahmud Abbas in Bethlehem.
The Israeli leg of his trip is already awash in controversy -- from a row over Trump's visit to Jerusalem's Western Wall, the holiest prayer site for Jews, to his alleged disclosure of Israeli intelligence to Russian officials.
Trump's meeting with Pope Francis -- two men at odds on everything from climate change to refugee policy -- remains highly unpredictable, although the pontiff says he will give America's bullish leader an open-minded hearing.
The president will also meet members of NATO in Brussels and attend a G7 summit in the picturesque Sicilian town of Taormina overlooking the Mediterranean.
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