A federal judge challenged special counsel Robert Mueller's prosecution of Paul Manafort, scolding prosecutors Friday for squeezing the former campaign manager to get information that would help impeach President Donald Trump.

"The vernacular is, 'to sing,'" Judge T.S. Ellis III, a Ronald Reagan appointee, told prosecutors in the Alexandria, Virginia, courtroom.

Ellis was hearing motion-to-dismiss arguments in the Virginia case, in which Mueller’s team has charged Manafort with filing false income tax returns, failing to report foreign bank accounts and bank fraud. The charges relate to work he did for the government of Ukraine.

"You don't really care about Mr. Manafort's bank fraud," Ellis said during the hearing. "You really care about getting information Mr. Manafort can give you that would reflect on Mr. Trump and lead to his prosecution or impeachment."

Ellis didn't rule on the motion, saying he wants to see unredacted versions of Deputy Attorney General Rod Rosenstein's orders assigning special counsel before he can issue a ruling. Ellis gave prosecutors two weeks to provide.

Ellis said special counsel should not have "unfettered power" to prosecute Manafort.

Prosecutors told Ellis their instructions from Rosenstein aren't just in the memos he seeks, but said some are secret and shouldn't be available for public scrutiny because of ongoing investigations and national security concerns.

Ellis seemed amused by that, framing the prosecution's case back to them, reported Jake Gibson of Fox News Channel.

"We said this is what the investigation was about but we are not bound by it and we were lying. C'mon, man!" Ellis said, using an expression often used by football announcers.