In blistering questioning, a defense lawyer accused the protege of former Trump campaign chairman Paul Manafort of being immersed in "so many lies" he can't remember them all, as he tried to undermine the credibility of the government's star witness in Manafort's fraud trial.
As for the bank fraud charges against Manafort, prosecutors presented the most compelling evidence yet that he knowingly inflated his income when applying for loans.
The aggressive questioning was aimed at shifting blame from Manafort onto Gates, who pleaded guilty in Mueller's investigation and agreed to cooperate with investigators by testifying in the financial fraud trial.
"After all the lies you've told and fraud you've committed, you expect this jury to believe you?"
Gates conceded it was "in excess of 50 to 100 years", but said any eventual sentence - including avoiding jail by receiving probation - would be up to a judge.
"WTF", Manafort wrote to Gates in one email shown to the jury.
Downing hinted that he wanted to get at the prosecution's questioning of Gates about what would happen to his plea deal if he lied from the witness stand.
Gates also admitted, however, that the same tricks he used to help doctor and falsify records for Manafort he also deployed for his own personal gain in order to covertly wire funds out of Manafort's offshore accounts to line his own pockets.
After Downing asked whether Gates told the special counsel about four extramarital affairs, the prosecutors quickly objected on the basis of relevance. Under the deal, he admitted to helping Manafort evade taxes, violate US lobbying laws, and hide foreign bank accounts.
Asked if he got any personal benefit from Mr Manafort's falsified loan applications, Gates responded: "No, I did not".
Ahead of that barrage, Gates implicated himself in a vast amount of criminal conduct on the stand, an apparent strategic decision by prosecutors as they hoped to take some of the steam out of the defense's questioning. He told jurors he embezzled from Manafort by filing false expense reports.
After saying Monday that he committed crimes with Manafort, including concealing offshore accounts to avoid reporting them to the US government at tax time and claiming false income to get loans, Manafort defense attorney Kevin Downing asked the witness, "This jury is just supposed to believe you after all the lies that you've told and the fraud you've committed?"
Manafort's accountant was asked about a purported $10 million loan from Russian oligarch Oleg Deripaska.
"In Cyprus, they were documented as loans".
Another email from February 2016 had Manafort conversing with Gates about a loan forgiveness letter that both Gates and an accountant have testified was fraudulent.
Downing then asked about what he called "the secret life of Rick Gates", inquiring whether Gates kept an apartment in London and if he engaged in an extramarital relationship there.
For this Manafort was paid US$4million a year, in quarterly payments of US$1million, Gates recalled, though at some point the currency switched from United States dollars to Euros. But Trump has shown interest in the proceedings, tweeting support for Manafort and suggesting he has been treated worse than gangster Al Capone.
In fact, his name was barely mentioned in the first five days of the tax and bank fraud case brought against his former campaign chairman. But then prosecutor Greg Andres invoked Trump's name, and Gates' and Manafort's work on the campaign became more explicitly tied to the alleged crimes at the heart of the trial. He also admitted to embezzling money from other employers in the past.
Gates said it was a "very common method" for Dr. K and that, once the money was moved into the accounts, Manafort decided what to do with it.
After Gates described his theft as "unauthorized transactions" instead of embezzlement, Downing prodded him to use the latter term - and Gates ultimately relented, saying, "It was embezzlement from Mr. Manafort".
For most of his testimony, Gates did not look at Mr Manafort, while the defendant stared intently at his former partner.