The controversial arrangement by the U.S. Air Force to refuel at a Scottish airport near President Trump’s Turnberry golf resort apparently was signed under the Obama administration, according to multiple reports.

The details emerged as the Air Force was called to explain a March stopover in the Scottish resort -- with Democrats on the House Oversight Committee writing to Acting Defense Secretary Patrick Shanahan as part of their investigation into alleged conflicts of interest by the president. The twist revealing that the airport deal predates his administration could boost Trump's case.

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Politico, which was among the outlets to publish stories this week examining the relationship between the Air Force and the resort, reported that the Air Force crews stayed at Trump’s Scottish resort up to 40 times since 2015.

It also reported that the contract with the Prestwick Airport was in fact signed during the Obama administration. The Washington Post also reported that the airport was sending visiting crews to Trump’s course before he ran for president.

The Air Force said in a statement that relatively few crews stayed at Trump Turnberry between 2015 and 2019.

“We reviewed the vast majority of the 659 overnight stays of Air Force crews in the vicinity at Glasgow Prestwick Airport between 2015 and 2019. Approximately six percent of those crews stayed at the Trump Turnberry,” the statement from an Air Force official said. “As a practice, we generally send aircrews to the closest, most suitable accommodations within the government hotel rate. The review also indicated that about 75 percent of the crews stayed in the immediate vicinity of the airfield and 18 percent stayed in Glasgow.”

The Post noted that no evidence has emerged to show Trump did anything to alter the existing arrangement since entering office. The New York Times, meanwhile, found that the deal involved the Air Force paying a discounted rate of as little as $130 a night, compared with a typical rate of more than $300 a night. It was one of 13 hotels booked by the airport, and is approximately 40 minutes away from the airport.

Trump has dismissed criticism on the issue, saying he had “nothing to do” with the stops.

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“I know nothing about an Air Force plane landing at an airport (which I do not own and have nothing to do with) near Turnberry Resort (which I do own) in Scotland, and filling up with fuel, with the crew staying overnight at Turnberry (they have good taste!). NOTHING TO DO WITH ME,” Trump tweeted on Monday.

Still, Trump continues to face concerns about other government functions at his properties, including the pitch to hold the next G-7 meeting at his Doral resort in Florida.

Democrats have indicated they are zeroing in on the administration’s use of Trump Organization properties, which they claim violates the Emoluments Clause and could feed their case for impeachment.

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Last week, Judiciary Committee Chairman Jerry Nadler, D-N.Y., penned a letter to White House Counsel Pat Cipollone and Secret Service Director James Murray seeking information about Trump’s “apparent promotion and solicitation of foreign and U.S. government business at Trump Organization owned or affiliated properties.”

Fox News' Lucas Tomlinson and Brooke Singman contributed to this report.