The House Oversight and Government Reform Committee opened an investigation as to why an Air National Guard crew stopped at President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE’s Turnberry resort in Scotland while traveling to Kuwait.

The probe, first opened in April, focuses on the unusual stopover the crew on the C-17 military transport plane made on both legs of the trip to deliver supplies, several people familiar with the incident told Politico. But the panel has yet to receive any answers from the Defense Department.

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“The Defense Department has not produced a single document in this investigation,” a senior Democratic aide on the oversight panel told The Hill. “The committee will be forced to consider alternative steps if the Pentagon does not begin complying voluntarily in the coming days.”

The Pentagon and Oversight Committee did not immediately respond to requests for comment from The Hill.

The oversight panel’s investigation is part of a broader inquiry into military spending at and around the Scotland property, according to Politico. The committee said in a letter to the Pentagon in June that was obtained by The Hill that the military has spent $11 million on fuel at the Prestwick Airport, the closest airport to Trump Turnberry, since October 2017 even though the fuel would be cheaper if purchased at a U.S. military base.

The news comes as the administration is under intense scrutiny over Vice President Pence’s decision to stay at Trump International Golf Links & Hotel in Doonbeg, Ireland, despite having meetings 182 miles away in Dublin, fueling Democratic concerns that the government has made moves to line Trump’s personal pockets.

Rep. Ted Lieu Ted W. LieuThe spin on Woodward's tapes reveals the hypocrisy of Democrats Larry Kudlow defends response to coronavirus: Trump 'led wisely' Lieu on Trump 'playing it down' on coronavirus: 'This is reckless homicide' MORE (D-Calif.), a vocal Trump critic, hammered the Pentagon over the C-17’s stop in Turnberry, saying it “smells like corruption.”