An unnamed U.S. congressman was mentioned in a criminal information docket for former Trump campaign aide Rick Gates pleading guilty on Friday to lying to U.S. investigators about a 2013 meeting involving former Trump campaign chairman Paul Manafort, his boss.

Public filings show that the day the meeting took place – March 19, 2013 – Manafort met with Russia-friendly Rep. Dana Rohrabacher of California.

The criminal information that was unsealed on Friday shows that Gates confessed he had falsely claimed he was unaware of any discussions from the meeting about Ukraine.

Manafort and Gates were indicted by a federal grand jury last fall on 12 charges related to the work they did in Ukraine before joining Trump's campaign, and were hit with a 32-charge indictment on Thursday.

Special counsel Robert Mueller has encouraged both men to cooperate with his probe, which is seeking to determine if the Trump campaign colluded with the Kremlin during the 2016 election. Manafort has so far given no indication that he will comply, but Gates has agreed to cooperate.

Information about the 2013 meeting first emerged in 2017 in supplemental filings from Manafort’s firm, DMP International, and another firm who had a partner participate.

A spokesperson for Rohrabacher downplayed the significance of the meeting, which also involved Vin Weber, a Mercury lobbyist and former congressman.

“As the congressman has acknowledged before, the meeting was a dinner with two longtime acquaintances – Manafort and Weber – from back in his White House and early congressional days,” the spokesperson said, according to Bloomberg.

“The three reminisced and talked mostly about politics,” the spokesperson added. “The subject of Ukraine came up in passing. It is no secret that Manafort represented [former Ukrainian President] Viktor Yanukovych’s interests, but as chairman of the relevant European subcommittee, the congressman has listened to all points of view on Ukraine.”

Capitalizing on the news Friday, Rohrabacher’s challenger in the 2018 midterm election said that voters have been pressing him for answers and demanded Rohrabacher “come clean.”

"District 48 remains predominately [sic.] a Republican district. And with every new Rohrabacher-revelation that hits the headlines, our phones start ringing,” Paul Martin said in a statement. “The Congressman will not hold a town hall meeting, so voters are coming to me for an explanation."

"My opponent calls Russia meddling a 'hoax.' He chastises Robert Mueller's investigation,” Martin added. “He lobbies on behalf of Vladimir Putin against Magnitsty [sic.] Act sanctions. He buddies up with white supremecists [sic.] and [WikiLeaks founder] Julian Assange. And now we know he was part of the Manafort-Gates meeting which is the subject of a criminal indictment."

In addition to pleading guilty to lying about the meeting, Gates also pleaded guilty this month to conspiracy against the U.S.