Special counsel Robert Mueller's team appeared to have a tough day in court on Friday as Judge T.S. Ellis was sharply critical of the prosecutors' grounds to bring their case against Paul Manafort — but perhaps the most important and informative part of the exchange went largely unnoticed.

The judge pushed the prosecutors on why they were bringing the case focusing on bank and tax fraud and against Manafort, President Donald Trump's one-time campaign chair, when it was so far afield of the original mandate that led to the creation of the special counsel.

As MSNBC's Rachel Maddow noted, the judge's question was a good one: "If the Michael Cohen case can just become a local prosecution case in New York, why can't the Paul Manafort case become a local prosecution case in D.C. or indeed Virginia?"

She continued: "So far we've seen nothing in the prosecutors' filings in the Manafort case that shows a connection to Russsian campaign interference in the presidential election. I mean, if the Manafort crimes are a separate, discrete matter, if they're all about his bank and tax fraud charges related to his work in Ukraine years ago, then why wouldn't those also be handed off to separate prosecutors?"

Quoting from the prosecutors' response to these types of questions, Maddow said: "'The special counsel's office takes very seriously the primary mission it was assigned in examining Russian interference in the 2016 election.'" It added that it would refer unrelated criminal activity to an unrelated office.

"Does that mean that these multiple felonies against Paul Manafort … [are] related to Russian interference in the 2016 election?" Maddow asked provocatively.

Watch the clip below: