Three appellate specialists working on special counsel Robert Mueller's investigation into Russian interference in the 2016 election made their argument debuts Thursday, defending the criminal charges against former Trump campaign chairman Paul Manafort in Washington's federal trial court.

As Manafort has fought against accusations anchored in Mueller's investigation into Russian interference in the 2016 election, the task of arguing in court generally has fallen to just a few lawyers between the two sides: defense lawyer Kevin Downing for Manafort and, from the special counsel's prosecution team, Andrew Weissmann and Greg Andres.

That changed on Thursday. During a hearing before U.S. District Judge Amy Berman Jackson, two attorneys on detail from the U.S. Solicitor General's Office—Michael Dreeben and Elizabeth Prelogar—defended the criminal charges. Additionally, Adam Jed, who joined Mueller's team from the civil appellate staff, made his argument appearance.

Dreeben, a top criminal law expert at the U.S. Department of Justice who has argued more than 100 cases before the Supreme Court, joined the special counsel's office shortly after U.S. Deputy Attorney General Rod Rosenstein selected Mueller to lead the investigation. But it was only two weeks ago, on April 6, that Dreeben entered a formal appearance in the special counsel's case against Manafort, who has been charged with money laundering and failing to register as a lobbyist for the Ukrainian government.

On Thursday, Dreeben argued against Manafort's position that the special counsel's office was given too broad a jurisdiction and that it has exceeded that expansive authority in the prosecution of Manafort.

Downing, a former partner at Miller & Chevalier, has repeatedly pointed out that Manafort's alleged misconduct is entirely unrelated to the 2016 presidential campaign. Also, he has taken aim at language in Mueller's appointment order that allows the special counsel to investigate matters that “arise directly from” the investigation into Russia's election interference.

Dreeben on Thursday defended that language in the original appointment order, saying it was meant “to reflect the fact that investigations are naturally going to move forward.”

Dreeben later said the special counsel's authority was confirmed by an Aug. 2 memo from Rosenstein, which specifically stated that Mueller's team could charge Manafort with crimes connected to his work for the Ukrainian government. Manafort's connections to Ukraine, Dreeben said, fell within the special counsel's mandate because they could have conceivably been used as back channels to Russia.

“Investigators will naturally look at those things,” he said.

Jackson heard argument for more than two hours on Thursday but did not immediately rule.

Manafort was in court with Downing and his two other defense lawyers, Thomas Zehnle and Richard Westling, a litigation and health care partner at Epstein Becker & Green, joined the defense team in March.

Westling's argument Thursday focused on the special counsel's allegation that Manafort violated the Foreign Agents Registration Act, a 1938 law that requires lobbyists for foreign governments and other entities to disclose their work to the Justice Department. The new focus on that law caused “sleepless nights” among members of Washington's influence market.

Manafort has a separate civil case, also in front of Jackson, that challenges the scope of Mueller's authority.

Read more:

Paul Manafort's Move to Restrain Mueller Meets Skeptical Judge

Paul Manafort Boosts Defense, Hiring Epstein Becker & Green's Richard Westling

Mueller Enlists Dreeben, Top Criminal Law Expert, for Russia Probe

Mueller Recruits Prelogar from Solicitor General's Office to Russia Probe

Ex-Skadden Associate Gets 30-Day Jail Sentence for Lying to Mueller's Team