(Reuters) - George Papadopoulos, a former aide to Donald Trump’s 2016 presidential campaign who pleaded guilty to lying to federal agents probing ties between the campaign and Russia, filed a motion on Friday seeking to postpone his sentence pending a separate case he hoped would lead to his conviction being overturned.

FILE PHOTO: Former Trump campaign aide George Papadopoulos leaves after his sentencing hearing at U.S. District Court in Washington, U.S., September 7, 2018. REUTERS/Yuri Gripas/File Photo

The motion was submitted by a new team of lawyers hired by Papadopoulos after his sentencing in September to 14 days in prison. The former campaign aide has in recent weeks turned critical on Special Cousnel Robert Mueller’s 18-month investigation and sought to raise funds for his legal bills.

In a court filing, Papadopoulos’ lawyers argued that their client should be able to put off his sentence, due to start on Nov. 26, while a separate case challenging the legality of Mueller’s appointment is ongoing. A three-judge panel hearing that appeal has not indicated when it may rule.

“If the appeal is successful, then the Special Counsel lacked constitutional authority to prosecute Mr. Papadopoulos in the first instance,” wrote lawyers at Pierce Bainbridge Beck Price & Hecht LLP, who now represent Papadopoulos, adding that in such an outcome his “conviction would be reversed.”

Gene Rossi, a Washington attorney and former federal prosecutor, described the motion as a long-shot.

“A snowball in hell has a greater chance of survival,” Rossi said, noting Papadopoulos waived his right to appeal. He also said he believed the courts would reject the legal challenges to Mueller’s authority.

According to the government’s sentencing memorandum, Papadopoulos lied to agents about his contacts with Russians during the campaign “to minimize both his own role as a witness and the extent of the campaign’s knowledge of his contacts.

Among those contacts were London-based professor Joseph Mifsud, who told him the Russians had “dirt” on Trump’s Democratic presidential rival Hillary Clinton in the form of “thousands of emails.”

Papadopoulos pleaded guilty in October 2017. At sentencing in September he told the judge that he had made a “dreadful mistake” and that he hoped to redeem himself.

But in recent weeks Papadopoulos has attacked the Mueller probe on Twitter and in media appearances as unjust and politically charged. Among his allegations is that Mifsud is tied to Western intelligence.

Peter Carr, a spokesman for Mueller, declined to comment.