Former Trump campaign foreign policy adviser George Papadopoulos must report to prison on Monday as scheduled, a judge ruled Sunday, denying his bid to delay his term until an appeals court rules in a separate lawsuit challenging the constitutionality of Special Counsel Robert Mueller's appointment.

In a 13-page ruling, Obama-appointed U.S. District Court Judge Randy Moss noted that Papadopoulos had forfeited most of his rights to contest his conviction when he became the first person to plead guilty in Mueller's probe into Russian interference in the 2016 election.

Papadopoulos "has failed to demonstrate that the D.C. Circuit is likely to conclude that the appointment of the Special Counsel was unlawful — and, indeed, he has failed even to show that the appeal raises a ‘close question’ that ‘very well could be decided’ against the Special Counsel,” Moss wrote, citing other decisions affirming Mueller's authority.

He continued: “Papadopoulos has not identified any extenuating circumstances — nor is the Court aware of any — that would overcome the presumption against granting such an eleventh-hour stay.”

Trump in recent days has lent support to the theory that Mueller has exceeded his legal authority from Congress, calling the probe an "illegal witch hunt" on Twitter. Acting Attorney General Matthew Whitaker, who now oversees Mueller as head of the Department of Justice, has argued that Mueller has come close to exceeding his statutory powers.

Papadopoulos was sentenced in September to 14 days in prison for lying to the FBI during Mueller’s investigation.

He was also sentenced to 13 months supervised release, 200 hours community service and a $9,500 fine. Before his sentencing, the former adviser said he was “deeply embarrassed and ashamed.”

“My entire life has been turned upside down. I hope to have a second chance to redeem myself,” he said. Mueller’s team had pushed for a six-month prison sentence, while Papadopoulos’ defense had requested probation.

But late last month, Papadopoulos told "Fox & Friends" that he was considering withdrawing the guilty plea, charging in an interview with host Brian Kilmeade that there was "tremendous misconduct" by the government in his case.

"Given certain information I learned just yesterday that I can't publicly disclose right now, I'm actually even considering withdrawing my agreement I have come to with the government," he said.

According to the indictment, Papadopoulos was told by a Maltese professor in April 2016 that Russian officials had “dirt” on Hillary Clinton in the form of “thousands of emails.”

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He later attempted to use his links to the professor and Russian nationals to attempt to set up a meeting between Trump and Russian President Vladimir Putin. He admitted to lying about those contacts to Mueller’s team, which investigators said led them to miss a chance to interview the professor, Joseph Mifsud.

His lawyer argued that the appellate case against Mueller's authority could constitute new evidence that could allow him to mount a challenge.

Last week, Trump submitted written answers to Mueller's questions in the ongoing Russia investigation, marking a major milestone in the long-running probe as it seemingly nears its conclusion.

The president also railed against "disgraceful" liberal judges who he says defy the law in concerted efforts to undermine his authority.

Meanwhile, former Infowars Washington Bureau Chief Jerome Corsi said in a livestream earlier this month that he expects to be indicted soon for perjury in the Mueller probe, which has already produced dozens of indictments since it began in May 2017.

Fox News' Adam Shaw and The Associated Press contributed to this report.