President Trump traveled to the United Arab Emirates on Thursday after visiting Al Udeid Air Base in Qatar, the largest U.S. military facility in the Middle East and considered “essential to regional security” by the Pentagon.

“I have nothing else to do,” Mr. Trump told U.S. troops from a stage at the base, “so let’s have a little fun.” In a rally-like atmosphere, he spoke about Qatar’s purchases of American military supplies and told several of his favorite stories, including one about his trip to Iraq during his first term.

Mr. Trump is making a four-day tour of Gulf states that began on Monday in Saudi Arabia and has focused on business deals and regional diplomacy, including a meeting on Wednesday with the new leader of Syria. Sheikh Tamim bin Hamad Al Thani, the emir of Qatar, effusively praised Mr. Trump, who in turn called his host a “great gentleman” and a “friend of mine.”

Neither leader mentioned it, but Mr. Trump plans to accept a luxury Boeing 747-8 as a donation from Qatar’s royal family to serve as Air Force One. There has been backlash from Democrats and even some of Mr. Trump’s supporters to the proposal, which raises extensive legal and ethical issues. The president has said he would be “stupid” not to accept the plane.

The U.S. military has been using Al Udeid since September 2001, when it positioned planes there to target the Taliban and Al Qaeda in Afghanistan. Two years later, Al Udeid became the main U.S. air operations hub in the region.

U.S. commanders used Al Udeid to coordinate a wide variety of missions during the wars in Iraq and Afghanistan, as well as strikes against ISIS in Syria. The Air Force has deployed a wide variety of aircraft there, from advanced fighters and long-range bombers to drones, transport planes and in-flight refueling tankers.