An aide to Roger Stone (Stone, above) must testify before a grand jury under subpoena from special counsel Robert S. Mueller III, the chief federal judge of U.S. District Court for the District of Columbia has ruled. (Mark Wilson/Getty Images)

A former aide to longtime President Trump confidant Roger Stone must testify before the special counsel’s grand jury, a federal judge in Washington ruled Thursday.

The judge rejected a challenge from Andrew Miller, a former assistant to Stone who tried to block subpoenas from special counsel Robert S. Mueller III in his investigation into Russian interference in the 2016 presidential election.

The redacted opinion from U.S. District Chief Judge Beryl Howell affirming the legal legitimacy of the special counsel’s appointment does not identify Miller by name, but his attorney confirmed that the ruling is in response to Miller’s request.

Howell’s ruling orders Miller to “appear before the grand jury to provide testimony at the earliest date available” and to provide subpoenaed records.

“We’re disappointed with the court’s ruling,” Miller’s attorney, Paul Kamenar, said in an interview. “But the judge obviously took our challenge to Mueller’s constitutionality seriously, as evidenced by the 93-page opinion.”

Miller’s attorneys had argued that Mueller “wields too much power with too little accountability” and was unlawfully appointed, according to Howell’s summary of Miller’s filing.

In her lengthy ruling, Howell said that the “witness raises legitimate questions, but his concerns are not legally sustainable.”

“The scope of the Special Counsel’s power falls well within the boundaries the Constitution permits, as the Special Counsel is supervised by an official who is himself accountable to the elected President,” she wrote, referring to Deputy Attorney General Rod J. Rosenstein.

Miller worked for Stone during the 2016 presidential campaign, handling duties such as setting up media interviews. He is one of at least a half-dozen of Stone’s associates to be called to testify. Others include his driver, John Kakanis, and a social media consultant, Jason Sullivan. And Kristin Davis, who gained notoriety in the 2000s as the “Manhattan Madam” when she ran a high-end prostitution ring, has said her attorney was told investigators want to question her.

Stone has accused Mueller’s team of harassing his associates. He declined to comment Thursday.

It remains unclear if and when Miller will appear before the grand jury. Kamenar said that the fight to block the appearance will continue and that he would explore an appeal.

Miller has not been given a date to appear before the grand jury, Kamenar said. He said he expects to have a better sense of what will happen next within a week.

Mueller’s prosecution team appears to have a continued interest in Stone, who has been under scrutiny for his contacts with the Twitter persona Guccifer 2.0. A recent indictment of 12 Russian intelligence officers by Mueller’s team alleges that Guccifer 2.0 was actually operated by a group of Russian military intelligence officers based in Moscow. In 2016, Guccifer 2.0 released some of the emails hacked from the Democratic National Committee and Hillary Clinton’s campaign chairman, John Podesta.

Stone has disputed the suggestion that Guccifer 2.0 is a tool of Russian intelligence, saying it has not been proved. He has said that he thought he was communicating with a Romanian hacker and that their exchanges were “benign,” including a Twitter direct message in which Stone congratulated Guccifer 2.0 for being reinstated after being banned by Twitter.

The filing from Miller’s attorneys is the latest to challenge the constitutionality of Mueller’s appointment. Attorneys for former lobbyist Paul Manafort, on trial this week in Virginia on bank and tax fraud charges, failed in their efforts. There is also a pending challenge from attorneys representing the Russian firm Concord Management and Consulting, which is accused of financially backing an alleged Russian Internet trolling operation accused of a massive campaign to disrupt the 2016 presidential election.