WASHINGTON – A panel of a federal appeals court asked Friday for the Justice Department and lawyers challenging the legitimacy of special counsel Robert Mueller to argue whether the firing of Attorney General Jeff Sessions affects their case.

The case focuses on whether Congress has authorized Mueller’s office and whether Deputy Attorney General Rod Rosenstein had the authority to appoint him to investigate Russian interference in the 2016 election. Rosenstein appointed Mueller after Trump fired FBI Director James Comey in May 2017.

Sessions recused himself because he worked on Trump’s campaign. Trump fired Sessions on Wednesday and replaced him with Acting Attorney Matthew Whitaker, who has been critical of Mueller’s investigation. Democratic lawmakers have called on Whitaker to recuse himself from the Mueller probe.

The case involved Andrew Miller, an associate of Roger Stone, a longtime friend of Trump, who was cited for contempt in refusing to testify before Mueller’s grand jury. Miller appealed to the U.S. Court of Appeals for the D.C. Circuit.

After a hearing Thursday, the three-judge panel – Karen Henderson, Sri Srinivasan and Judith Rogers – asked Friday for lawyers on both sides whether the change from Sessions to Whitaker had any impact on the case. Briefs are due Nov. 19.

Neal Katyal, a former solicitor general who argued government cases before the Supreme Court, tweeted that it’s possible that the court could rule that Rosenstein is the proper person to oversee the Mueller investigation, despite Whitaker's appointment.

More:Sessions ouster fuels fear Trump is trying to impede Robert Mueller's probe

More:Who is Matthew Whitaker? Hawkeye football star and federal prosecutor becomes acting attorney general

More:Democratic House to bolster Robert Mueller probe, revive Russia inquiries in Congress