Thomas Lindenfeld, once part of Congressman Chaka Fattah’s inner circle, faced his longtime friend and associate Wednesday in federal court as one of two key witnesses called by prosecutors in Fattah’s RICO trial.

Sources say Lindenfeld, as well as Fattah’s longtime aide and close confidant Gregory Naylor, are essentially the linchpins of the government’s corruption case against Fattah.

Under direct examination by Assistant District Attorney Eric Gibson, Lindenfeld appeared calm on the witness stand, having already pleaded guilty in November 2014 to wire fraud. He has agreed to cooperate with the government in exchange for a lighter sentence. He faces up to 20 years behind bars.

RELATED: Prosecutor calls Chaka Fattah a thief as racketeering trial gets underway

During testimony Tuesday on day two of the trial, Al Lord, CEO of the student loan lender Sallie Mae, testified that he lent Fattah $1 million to help push his faltering 2007 mayoral campaign over the hump. On Wednesday, Lindenfeld said he got a call from Al Lord's assistant, two weeks before the 2007 mayoral primary, and Fattah had "some ideas with how to deal with it."

"It was going to be a loan," he said. 

“Were you expected to pay it back?” Gibson asked.

“The congressman said it was no problem."

“Would you have done this if this was supposed to be repaid with your money?"

“No. I had the word of the congressman. I thought that was adequate.”

Early on, when Lindenfeld had what he called “kitchen cabinet” conversations with Fattah, Washington, D.C., powerhouse political consultant David Axelrod, co-defendant Bonnie Bowser, and occasionally former Mayor John Street, among others, Lindenfeld said he told Fattah that he had reservations about his fundraising abilities.

In the transitioning period from “kitchen cabinet” discussions to actually creating an exploratory committee for the 2007 mayor’s race, Lindenfeld wrote to Fattah, “I’ve razzed you about being … the least proficient fundraiser among all members of Congress.”

With two weeks left until primary day in 2007, Lindenfeld – never looking at the congressman while on the stand – testified that the Fattah campaign had not spent all of Lord’s money, and he was happy about that, because he knew that would mean they would have that little left to repay.

“I was resistant [to spend it],” said Lindenfeld. “The less debt, the easier to pay it back…but there was a need for money on Election Day, too.”

RELATED: Fattah trial to begin on Monday

But Lindenfeld said Fattah was in charge of the checkbook. The campaign did return some money to Lord – $400,000 was repaid.

“You knew it was illegal at the time, is that right?” Gibson asked. 

“That’s right. We spent it according to instructions from the congressman, based on how he wanted it spent on the campaign.”

“Was there any serious effort by the congressman to get this debt repaid?” 

“Not that I could tell.”

The defense begins cross-examination Thursday morning.