Gates, who testified Monday and returned to the witness stand Tuesday, detailed years of alleged lawbreaking at Manafort's political firm and admitted to stealing money from secret overseas bank accounts.
Manafort also falsely classified another $1.5 million in income as a loan, Welch testified - while adding that Manafort never indicated he had foreign bank accounts on his tax returns.
The accountant testified she was unaware if the loan was recognized as income or ever paid back.
Testimony resumes Thursday at 9:30 a.m. ET in Alexandria, Virginia, and the government is expected to rest by Friday.
Gates struck a deal with special counsel Robert Mueller in February, pleading guilty to one count of conspiracy against the United States and one count of making false statements to the Federal Bureau of Investigation.
On the seventh day of former Trump campaign chairman Paul Manafort's criminal trial, the prosecution wasn't ready to rest.
"I'm not happy with this judge", Napolitano said on "The Daily Briefing" on Wednesday.
Defense lawyer Kevin Downing began his cross-examination of Gates on Tuesday, accusing Gates of being immersed in "so many lies" he can't remember them all and demanded to know how a jury could possibly trust him.
Downing accused Gates of using the funds he admitted to stealing from Manafort to pay for a lavish lifestyle that included a London apartment and travel funds to finance one of his extramarital affairs.
Prosecutors had braced for the tough questioning by getting Mr Gates to come clean about his own crimes. And the fact that after loaning Manafort millions of dollars Calk became an economic adviser to Trump casts doubt on Trump's famous pledge to "drain the swamp" and puncture the rampant influence peddling in Washington. "I thought he was needlessly evasive and argumentative", said Barbara McQuade, a former U.S. Attorney in MI who has been watching the trial and said she observed jurors reacting with negative body language as he testified.
While Gates and others have pleaded guilty, Manafort has refused to strike a deal and legal experts say he may be holding out hopes of a pardon from Trump. "I'm taking responsibility for it".
The questioning is part of the Manafort defense strategy of presenting Gates to the jury as someone who lies and can not be trusted.
He badgered Gates into admitting that he had engaged in an extramarital affair with a woman in London roughly 10 years ago and briefly questioned Gates about three other affairs before prosecutors objected.
Rick Gates has finished his testimony in the financial fraud trial of his former boss, Paul Manafort, after one last effort by defense lawyers to erode his credibility. But Trump has shown interest in the proceedings, tweeting support for Manafort and suggesting he has been treated worse than gangster Al Capone.
Prosecutors on Wednesday planned to call an Federal Bureau of Investigation forensic expert who traced Manafort's accounts.
Gates added that Manafort also wanted to give the businessman a heads-up about the FBI's interest in the offshore accounts as part of the US government's efforts to recover assets stolen under former Ukrainian President Viktor Yanukovych.
In one exchange published in court Wednesday, Manafort instructs his Cypriot lawyer, Kypros Chrysostomides - referred to in court as "Dr. K" because, according to Gates, his name is hard to spell and pronounce - to transfer money from the Manafort-controlled Leviathan Ltd. He also is accused of fraudulently obtaining millions more in bank loans, including while he was working on the Trump campaign.
After Yanukovych lost power in 2014, "I would say it decreased the income stream", Gates, wearing a blue suit, told the court matter-of-factly. "They may think he's a sleazebag - but that's not going to make them overturn how they view the documents", the former attorney said.