Attorneys for Paul Manafort, the convicted former chairman of Donald Trump's presidential campaign, asked a federal judge Monday to sentence the longtime political consultant to a prison term "substantially below the statutory maximum" of 10 years.

In documents filed in federal court in Washington, D.C, attorneys Kevin Downing, Thomas Zehnle and Richard Westling said prosecutors had presented Manafort "as a hardened criminal who 'brazenly' violated the law and deserves no mercy." In fact, they argue, Manafort committed "garden-variety" and "esoteric" crimes by illegally lobbying for a pro-Russian political party in Ukraine, "failed to report to the government the source and total amount of income he made from those activities, and he attempted to conceal his actions from the authorities."

The documents also alleged that Special Counsel Robert Mueller prosecuted Manafort because he was "unable to establish that Mr. Manafort engaged in any Russia collusion" and claimed that Manafort had been "widely vilified in a manner that this country has not experienced in decades."

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Manafort pleaded guilty this past September to one count of "conspiracy against the United States" and one count of conspiracy to obstruct justice. He faces up to five years in prison on each count.

The plea came ten days before he was due to go to trial in a Washington federal court on seven counts of foreign lobbying violations and witness tampering.

"Mr. Manafort has been punished substantially, including the forfeiture of most of his assets," the lawyers added. "In light of his age and health concerns, a significant additional period of incarceration will likely amount to a life sentence for a first time offender."

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Earlier this month, U.S. District Judge Amy Berman Jackson ruled that Manafort had violated his plea deal with prosecutors by lying to federal agents about several subjects, including about his interactions with Konstantin Kilimnik, a business associate who the U.S. said had ties to Russian intelligence. Manafort hasn't been accused of any crimes related to Russian election interference, but court papers have revealed he gave Kilimnik polling data related to the Trump campaign during the 2016 election. A Mueller prosecutor also said that an August 2016 meeting between the two men went to the "heart" of the Russia probe. The meeting involved a discussion of a Ukrainian peace plan, but many other details about it have been redacted in court papers.

In addition to the case in Washington, Manafort faces the possibility of over 19 years in prison in a separate tax and bank fraud case in federal court in Virginia. A jury in that case convicted him of eight felony counts this past August.

Judge Jackson will sentence Manafort on March 13.

The Associated Press contributed to this report.