A federal judge on Sunday ordered former Trump campaign adviser George Papadopoulos to begin his two-week sentence Monday for lying to the FBI, denying his attorney's last attempts to postpone his incarceration.

Papadopoulos' legal team filed two motions – one on Nov. 16 and another Nov. 21 – in an effort to delay his sentence until another case, which challenges the constitutionality of special counsel Robert Mueller's appointment to investigate Russian election meddling in the 2016 election, has been decided.

Mueller's team urged U.S. District Judge Randolph Moss to deny Papadopoulos' request in a court filing Wednesday. Moss agreed with Mueller and denied both of Papadopoulos' motions. He said the time for Papadopoulos to file an appeal had expired and it was unlikely the case challenging Mueller's appointment could succeed.

Papadopoulos pleaded guilty last year to lying to the FBI about his Russian contacts while working for the Trump campaign in 2016. In September, he was sentenced to two weeks in prison, a year of supervised release, 200 hours of community service and a $9,500 fine. Moss ordered Papadopoulos to turn himself in to the Bureau of Prisons on Monday, as outlined in his plea deal.

Papadopoulos began working as a foreign policy adviser to the Trump campaign in March 2016. He is the first former Trump aide to be sentenced in connection to Mueller’s investigation.

According to Mueller's team, Papadopoulos "lied to the FBI regarding his interactions with a foreign professor whom he understood to have significant ties to the Russian government, as well as a female Russian national."

Papadopoulos allegedly told the FBI the professor was "a nothing" and his meetings with him happened before he started working on the Trump campaign.

"In truth and fact, the defendant knew that the professor took an interest in him only after the professor learned the defendant was affiliated with the Trump Campaign, and in late April 2016 after returning from a trip to Moscow, the professor told the defendant that Russia possessed 'dirt' on (Hillary) Clinton in the form of 'thousands of emails,' " Mueller's team said in a court filing.

Similarly, Papadopoulos said that his interactions with a Russian woman – who he claimed in an email was the niece of Russian President Vladimir Putin – happened before the campaign and that they were not important. He actually began communicating with her after he joined the campaign and tried to get her to set up meetings between the campaign and Russian officials.

Papadopoulos' lawyers argued it would be "unjust" for their client to serve his two-week sentence only to have Mueller's appointment declared unconstitutional in another case. Moss said Papadopoulos is not a part of that case and that two other judges had "issued thorough and carefully reasoned opinions rejecting the arguments that Papadopoulos now champions." Those arguments challenged Deputy Attorney General Rod Rosenstein's authority to appoint Mueller.

Moss said the chance that the U.S. District Court for the District of Columbia "will reach a contrary conclusion is remote."

The judge pointed out that the time for Papadopoulos to file an appeal expired Sept. 25 and that nothing in the Bail Reform Act cited by his lawyers calls for postponing someone's sentence pending the resolution of "an appeal brought by a different party in a different case."

Since pleading guilty in exchange for a reduced sentence – lying to the FBI could carry a sentence of up to five years in prison – Papadopoulos has publicly insisted he was "framed" and said he should not have agreed to the deal.

Papadopoulos posted tweets accusing "the Obama CIA, British intelligence and Australian intelligence plotting to sabotage Trump and his team with orchestrated 'Russia' meetings" and identifying those he said were "spying" on him and the campaign.

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