Gates appeared nervous on the witness stand at the court in Alexandria, Virginia, blinking frequently, his throat apparently dry as he spoke.
On Tuesday, Gates was forced to answer questions about past infidelity, his embezzlement and what Manafort had directed him to do while in his employment. He's expected to go for at least another hour in questioning with Manafort's attorney's.
He also admitted he had flown first class and stayed in luxury hotels during the relationship, using money embezzled from Manafort.
Manafort's defense team's primary strategy has been to pin much of the blame for financial crimes on Gates, and some observers felt Downing made some headway toward that goal on Tuesday.
Prosecutors will likely draw Gates back to those facts and away from his own misbehavior on redirect examination.
Prosecutors had braced for the tough questioning by getting Gates to come clean about his own crimes. The special counsel's office has pushed back against the leak allegation, and while an Federal Bureau of Investigation agent testified he was present at a meeting with AP reporters about Manafort, the agent said the AP was offered little more than a "no comment" and an acknowledgement that their reporters were generally on track.
Gates admitted during testimony on Monday to embezzling money from Manafort.
"While the firm believes that her actions were related only to work she performed for Mr. Manafort, and that no other client was affected, a detailed, independent internal review is being conducted to confirm that her activity was isolated", the firm said in the statement.
Manafort and Gates were the first two people indicted in special counsel Robert Mueller's investigation into potential ties between Russian Federation and the Trump campaign.
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In one example, Manafort and Gates emailed each other copies of a doctored profit and loss statement they later sent a bank to help Manafort obtain a loan. "I already admitted on the record that I took unauthorised funds from Mr Manafort". "I'm trying to change".
The 46-year-old former political consultant told jurors how Manafort asked for tickets to Trump's inauguration so he could give them to a banker involved in approving a loan at the center of his financial fraud trial.
It's a day that featured testimony from just one witness, Rick Gates, Manafort's longtime deputy, who finished his direct questioning from prosecutors and underwent a grueling cross-examination from lead defense attorney Kevin Downing.
The email from Manafort came after Gates informed him that the tax accountants had calculated that Manafort would have an increase in taxes of about $509,000 in 2014.
A clothier said he sold Manafort more than $900,000 in suits, a bookkeeper says she helped disguise foreign income as a loan to reduce Manafort's tax burden and, on Wednesday, an Federal Bureau of Investigation forensic account said Manafort hid more than 30 offshore accounts in three types of currencies from the IRS.
Gates also said that he did not report 15 foreign offshore bank accounts to the government.
"I acknowledge I had a period of time when I had another relationship", said Gates, who is married and has four children.
Through emails and documents submitted into evidence Tuesday, Gates explained how he and Manafort enlisted the help of a Cypriot lawyer - referred to in court as "Dr. K" because his name, Gates said, was hard to pronounce - to create "shelf" companies to receive payments from Manafort's various Ukrainian political clients for their work. "We need to discuss Steve Calk for Sec (retary) of the Army", Manafort wrote to Gates in an email on November 24, 2016. But inside the courtroom, trial proceedings had plodded along almost Trump-free.
Downing seized on those admissions to try and cast doubt on whether the jury can trust Gates' claims that he only carried out the fraud alleged by prosecutors at Manafort's behest.