Story highlights A judge ordered a witness to testify before the Mueller grand jury

The witness had tried to argue Mueller's appointment was unconstitutional

(CNN) A federal judge has rejected an attempt from an associate of Roger Stone to challenge a subpoena on the grounds that special counsel Robert Mueller's appointment was unconstitutional.

Andrew Miller, a former associate of longtime Donald Trump confidante Stone, was ordered to testify before the Mueller grand jury. Miller had challenged a subpoena for documents and testimony by arguing that Mueller's appointment was unconstitutional.

"Multiple statutes authorize the Special Counsel's appointment, and the official who appointed the Special Counsel had power to do so. For these reasons ... the witness's motion to quash the grand jury subpoenas is denied," US District Court for the District of Columbia Chief Judge Beryl Howell wrote in a 93-page opinion signed July 31.

Howell ordered the witness to appear for testimony "at the earliest date available to the grand jury, and to complete production of the subpoenaed records promptly."

Nearly two weeks ago, at least five prosecutors from Mueller's office and two attorneys representing Miller spent almost 90 minutes in a sealed court proceeding before Howell.

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