A federal judge in Virginia suggested he may side with Paul Manafort, the former chairman of President Donald Trump's 2016 campaign, in his motion to dismiss one of the two indictments against him in the Russia investigation.

Manafort's lawyers argue that the charges in the indictment are not valid because they do not relate specifically to collusion with Russia.

US District Court Judge T.S. Ellis III also suggested the special counsel Robert Mueller's office had brought the charges against Manafort to get him to flip against Trump.

A federal judge in Alexandria, Virginia, expressed deep skepticism Friday about the validity of one of the indictments against Paul Manafort, the former chairman of President Donald Trump's 2016 campaign.

Manafort is the subject of two indictments from the special counsel Robert Mueller's office.

The first, brought in Washington, DC, accuses Manafort of money laundering, failure to register as a foreign agent, and making false statements to investigators. The other, brought in Virginia, charges him with tax fraud, bank fraud, and failing to report foreign bank accounts.

Most of the charges against Manafort relate to his lobbying work for the Ukrainian government and pro-Russian interests.

Manafort appeared in court early Friday to seek the dismissal of the charges outlined in the Virginia indictment. The judge appeared receptive, at least in part, to Manafort's lawyer's argument that because the counts are not directly related to the Russia investigation, they should be dismissed.

According to BuzzFeed News' Zoe Tillman, US District Court Judge T.S. Ellis III suggested that the reason prosecutors were going after Manafort was to try to get him to flip on Trump.

"I don't see what relation this indictment has with what the special counsel is authorized to investigate," Ellis told prosecutors. "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."

Ellis later quipped: "The vernacular is 'to sing.'"

Manafort and his lawyers have mounted an aggressive defense in recent months. The core pillars of their argument are that:

Mueller's mandate in the Russia investigation is too broad.

Mueller overstepped his authority by charging Manafort with crimes unrelated to collusion with Russia.

Mueller is investigating whether the Trump campaign colluded with Moscow to tilt the 2016 race in his favor and whether Trump sought to obstruct justice when he fired FBI Director James Comey last May.

In appointing Mueller that month, Deputy Attorney General Rod Rosenstein gave him broad authority not only to investigate "any links and/or coordination between the Russian government and individuals associated" with the Trump campaign, but also to examine "any matters that arose or may arise directly from the investigation."

Earlier this year, it surfaced that Rosenstein also sent a memo to Mueller in August outlining the full scope of his mandate and specific threads he was allowed to investigate.

Per the memo, Mueller is authorized to investigate two threads related to Manafort:

Whether Manafort colluded with Russian government officials as Russia was trying to meddle in the 2016 US election.

Whether he committed any crimes "arising out of payments he received from the Ukrainian government before and during the tenure of President Viktor Yanukovych."

Prosecutors said Friday that their investigative powers were outlined both in Rosenstein's letter appointing Mueller in May and in the August memo. They also said they had additional authority that they could not disclose in the courtroom because it related to ongoing investigations and could affect national security.

But Ellis apparently wasn't buying it, reportedly characterizing the special counsel's office's argument as: "We said this was what the investigation was about, but we are not bound by it, and we were lying."

"Come on, man!" Ellis said.

Legal experts questioned the judge's comments.

Asha Rangappa, a former FBI special agent, characterized Ellis' remarks about prosecutors aiming to get Manafort to flip as "bizarre commentary."

"Unless there is something legally amiss in the indictment, speculating re motives of the [special counsel] is beyond the judge's purview (and also seems to suggest that there is a connection [between] Manafort's criminal bank fraud and Trump," she tweeted.

Renato Mariotti, a former federal prosecutor, echoed that view.

"Whether the special counsel wants Manafort to flip is not relevant to the question of whether this indictment is within the scope of his jurisdiction," he wrote. "If the judge considers Mueller's motivation in bringing the indictment and dismisses it, that's reversible error."

He added: "Even if the judge ultimately does not take his view of Mueller's motivations into account in his ruling, he politicized the proceeding with comments that were unnecessary and created an appearance that he has a political agenda."

Ellis did not immediately rule on Manafort's motion to dismiss the Virginia indictment. A trial date in the case is set for July 10.