US District Judge T.S. Ellis suggested that Mueller was pressing Manafort on unrelated charges in the hopes that he would provide incriminating information against President Donald Trump.

"I don't see what relation this indictment has with what the special counsel is authorized to investigate," Ellis said in court on Friday. "You don't really care about Mr. Manafort's bank fraud. ... What you really care about is what information Mr. Manafort could give you that would reflect on Mr. Trump or lead to his prosecution or impeachment."

Mueller’s investigation is tasked with looking into alleged collusion between the Trump campaign and Russia in the runup to the 2016 election. Manafort worked for the Trump campaign between March and August that year. He was indicted in Virginia on tax and bank fraud charges dating back to 2005 and 2007, and in Washington, DC, on charges of failing to properly register his lobbying work for the Ukrainian government between 2006 and 2015.

“The vernacular is to ‘sing',” Ellis said. “What you got to be careful of is, they may not only sing, they may compose.”

One of Mueller’s prosecutors, Michael Dreeben, argued that the bank fraud indictments fell under the scope of the Russia probe.

“Bank fraud in 2005 and 2007? Tell me how!” the judge shot back.

Dreeben told the judge that the probe was authorized last August by Deputy Attorney General Rod Rosenstein in a highly redacted memo. The redactions, Dreben argued, were made for national security reasons.

Ellis accused Mueller’s team of “not really telling the truth” about their probe into Manafort. “C’mon, man!” said Ellis, when Dreeben didn’t respond.