United States President Donald Trump's former campaign chief Paul Manafort was sentenced to nearly four years in prison by a federal judge on Thursday for tax crimes and bank fraud in the highest profile case yet stemming from Special Counsel Robert Mueller's Russia investigation.

Judge T.S. Lewis immediately came under fire from Democratic lawmakers for imposing what they described as a relatively light sentence on the 69-year-old Republican political consultant and lobbyist.

Prosecutors from the special counsel's office had argued for a stiff prison term for Manafort, the first target of the Mueller probe to be convicted in a criminal trial.

Ellis said that while Manafort had committed “very serious crimes,” he had previously led an “otherwise blameless life” and the advisory sentencing guidelines calling for 19 to 24 years behind bars were “excessive” and disproportionate to sentences for similar offenses.

“The government cannot sweep away the history of all these previous sentences,” the judge said.

Manafort was convicted by a jury in August of five counts of filing false income tax returns, two counts of bank fraud and one count of failing to report a foreign bank account.

He is one of a half-dozen former Trump associates and senior aides charged by Mueller, who has been investigating Russian meddling in the 2016 election and possible collusion with the Trump campaign.

The charges against Manafort were not connected to his role in the Trump campaign, which he headed for two months in 2016, but were related to lucrative consulting work he did for Russian-backed Ukrainian politicians from 2004 to 2014.

Prosecutors alleged that Manafort used offshore bank accounts to hide more than $55 million he earned working for the Ukrainians.

The money was used to support a lavish lifestyle which included purchases of luxury homes and cars, antique rugs, and expensive clothes, including an $18,500 python jacket.

His conviction was a stunning downfall for a man who also worked on the White House bids of Gerald Ford, Ronald Reagan, George H.W. Bush and Bob Dole.

Speaking from a wheelchair and wearing a green prison jumpsuit with the words “Alexandria Inmate” on the back, Manafort told the court that his “life, professionally and personally, is in a shambles.”

'Pain and shame'

I feel the pain and shame,” said Manafort, who the defense says suffers from gout. “To say that I feel humiliated and ashamed would be a gross understatement,” he said.

Judge Ellis said he did not hear Manafort express regret or remorse but he said the sentencing guidelines were “way out of whack”.

“I think what I've done is punitive,” Ellis said. He sentenced Manafort to a total of 47 months in prison for the eight counts and credited him with nine months of time served.

Manafort was ordered to pay $24 million in restitution and a $50,000 fine. Manafort still faces sentencing in a money laundering and witness tampering case in Washington next week, where the maximum penalty is 10 years and the judge has appeared more sympathetic to prosecutors.

'Accepts responsibility'

Defense attorney Kevin Downing, speaking after the sentencing, said Manafort “accepts responsibility for his conduct”.

“And I think most importantly, what you saw today is the same thing that we had said from day one — there is absolutely no evidence that Paul Manafort was involved with any collusion with any government official from Russia,” Downing said.

Adam Schiff, the Democratic chairman of the House Intelligence Committee, described Downing's remarks as a “deliberate appeal for a pardon” from Trump, who has denied any collusion with Russia and has denounced the Mueller probe as a “political witchhunt”.

“The statement by Paul Manafort's lawyers after an already lenient sentence — repeating the President's mantra of no collusion — was no accident,” Schiff said.

“One injustice must not follow another.”

Trump has dangled the possibility of pardons for some of those indicted by Mueller — including Manafort, whom he has praised as a “good man” who has been treated unfairly.

Minnesota Senator Amy Klobuchar, a candidate for the 2020 Democratic presidential nomination, also denounced the sentence.

“His crimes took place over years and he led far from a 'blameless life,” Klobuchar said on Twitter.

“Crimes committed in an office building should be treated as seriously as crimes committed on a street corner.”

During Manafort's trial, much of the damaging testimony against him was provided by his former deputy Rick Gates, who reached a plea deal with the special counsel's office.

Besides Manafort and Gates, four other former Trump associates face charges or have pleaded guilty to charges stemming from the Mueller investigation.

Former National Security Advisor Michael Flynn pleaded guilty to lying to the FBI about his contacts with Russian officials and is awaiting sentencing. Trump's former personal attorney Michael Cohen is to begin serving a three-year prison sentence on May 6 for fraud, tax evasion, illegal campaign contributions and lying to Congress.

George Papadopoulos, a foreign policy advisor to the Trump campaign, pleaded guilty to lying to the FBI and was sentenced to two weeks in prison. Another Trump advisor, Roger Stone, awaits trial.