First lady Melania Trump walks out of the East Room of the White House in Washington, Friday, May 12, 2017, after speaking to military mothers during a Mother's Day celebration.
First Lady Melania Trump was due to accompany Mr Trump and speak to United States soldiers.
Saudi Arabia will be Trump's initial stop on his first global trip as president, signifying the new USA administration's intent to reinforce its relationship with a top ally in the Middle East, particularly on security matters.
The president also plans to travel to Israel, the Vatican, Brussels and Sicily.
Be Civil - It's OK to have a difference in opinion but there's no need to be a jerk.
After visiting Saudi Arabia, Trump will fly to Israel for meetings with Prime Minister Benjamin Netanyahu and then to the Vatican in Rome, where he will seek an audience with Pope Francis before heading to Brussels for a North Atlantic Treaty Organisation summit, talks with European Union leaders, and then a meeting of the G-7 industrial nations in Sicily.
"First, he steps on himself constantly".
Asked point-blank if he'd done anything that might merit prosecution or even impeachment, he said no and then added concerning the allegations and questions that have mounted as he nears the four-month mark of his presidency: "I think it's totally ridiculous".
The White House touts a "historic" trip during which Trump - in visits to Saudi Arabia, the Vatican and Jerusalem - will reach out to leaders of the world's major monotheistic faiths. "Will be strongly protecting American interests - that's what I like to do!"
Donald Trump said the appointment of a special prosecutor to take over the Justice Department's probe into alleged ties between Russian Federation and the Trump campaign "hurts our country terribly".
The combination of tough talk on Shiite Iran, a lower-key focus on human rights, and the likely announcement of new arms deals should in theory earn the USA leader a warm welcome.
Among Trump's senior White House advisers are several former campaign officials, including his son-in-law Jared Kushner, Steve Bannon, Stephen Miller and Kellyanne Conway.
National security adviser H.R. McMaster told reporters on Thursday that Trump would deliver a speech in Saudi Arabia expressing hope that a peaceful vision of Islam would resonate worldwide.
He is due to visit the Church of the Holy Sepulchre as well as the Western Wall before holding talks with Israeli Prime Minister Benjamin Netanyahu.
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. As David Urban, the president's campaign leader, told CNN: "The president is going to the Middle East to let our friends know that we are back and to let our enemies know that we have returned". Trump told his almost 30 million followers on Tweeter hours before he boarded Air Force One along with his top officials and a battery of White House reporters from Joint Andrews Air Force Base.
A respected figure in American law enforcement circles, Mr Mueller headed the Federal Bureau of Investigation from 2001 to 2013, serving under Presidents George W Bush and Barack Obama.